Pochettino said: “I think today we showed that this wasn’t a team that had played well through the whole season.
“I think this was my worst day as a manager in England or Spain.”
Spurs, who had 62.5% of the possession, were repeatedly caught out on the break by their opponents, who had already been relegated.
They were 2-0 down at half-time, but hopes of a recovery increased as first Erik Lamela pulled one back, and then Newcastle striker Aleksandar Mitrovic was sent off.
Instead, Tottenham conceded a penalty, converted by Georginio Wijnaldum, before two late goals saw Newcastle complete a stunning win. The result left Pochettino’s side third in the Premier League.
When asked about what Newcastle manager Rafael Benitez said to him at the end of the game, Pochettino said: “It was strange – Newcastle are relegated but he felt sorry for me.”
Arsenal’s second place was their best placing in the Premier League since the 2004-05 season.
An Olivier Giroud hat-trick helped the north London side sweep aside relegated Villa for their 20th victory of the campaign.
On hearing the result at St James’ Park, Gunners fans celebrated ‘St Totteringham Day’ on social media – the point in the season where Spurs can no longer finish above Arsenal.
Their manager Arsene Wenger played down the achievement, saying: “We don’t start the season and think we want to finish above Tottenham but today we played with the only target we had. Today the aim before the game was to finish second.
“We achieved it. For a while our supporters were not going home very happy and today at least they had some satisfaction.”
In many ways, Manchester City’s display at the Liberty Stadium was a fitting way to end an underwhelming season that began with such promise before limping to a satisfactory but below-par conclusion.
Iheanacho – the on-field embodiment of a potentially exciting future – again demonstrated his sharpness in front of goal to poke home the opening goal after a Sergio Aguero shot had been saved in the fifth minute.
It was the 19-year-old’s 14th goal of the season and his eighth from his first 12 shots on target in the Premier League.
But he and his side failed to build on it, missing numerous chances to put the game to bed, with the young forward and his usually lethal Argentine partner Aguero particularly wasteful.
It left them vulnerable to a Swansea equaliser – which came courtesy of a 25-yard Ayew free-kick that deflected in off Fernando’s head – and a potentially devastating second in a tense second half for the away side.
Pellegrini tamely signs off
In securing a top-four finish, Pellegrini has achieved the very minimum required of him before handing over to Pep Guardiola this summer, but it does not mask the failings of the Chilean’s final campaign.
Despite winning the League Cup for a second time in three years and going further in the Champions League than ever before, City’s expensively assembled squad have underachieved in the league.
Their haul of 66 points is their lowest in the top-flight since the 2008-09 season – the first under Sheikh Mansour’s ownership.
Pellegrini leaves the Etihad with a league title to his name, the best win percentage of any Premier League manager barring Sir Alex Ferguson and Jose Mourinho and as the only City boss to have never finished below United.
But after starting so strongly, his reign has limped to its conclusion with a squad in need of an overhaul.
Stubborn Swansea make a point
In their previous two matches, Swansea had ended the top-four hopes of both Liverpool and West Ham.
Despite resting goalkeeper Lukasz Fabianski, captain Ashley Williams and top scorer Gylfi Sigurdsson and being without Ki Sung-yueng because of his military service in South Korea, boss Francesco Guidolin came close to making it a hat-trick.
Since the Italian joined the club in January, the Swans have improved significantly, losing only five of his 16 matches in charge.
And they once again demonstrated their newly acquired stubbornness to extend their unbeaten home run to five games, during which they have conceded just twice.
Having tied Guidolin down to a two-year deal this week, the Swans will be optimistic of building on this next season and avoiding the kind of poor form that prompted his arrival.
Man of the match – Jordi Amat (Swansea)
What they said
Swansea boss Francesco Guidolin: “I am happy because the moment was not simple in January [when he took over]. Now we have a comfortable position in the table. I am happy. I am proud. My players deserve this position because we have a good team.”
“It was a good performance, a good result, against in my opinion he best team in the Premier League in terms of quality, a lot of big, big players. And the game was good, we played well.
“I am happy, now. Only this for us and our players. This is a good memory.”
Manchester City manager Manuel Pellegrini to BBC Sport: “I wanted to win the Premier League this season, but the atmosphere from February when the club announced the new manager was maybe not the best atmosphere.
“We lost two important games at home when we were three points behind the leaders.
“The only option we had today was that we needed to get the point to get Champions League for next year.”
Manchester City goalkeeper Joe Hart, speaking to BBC Sport: “It is not what we set out to do at the start of the season but we will have to take it (fourth place).
“It was strange day, getting the job done, barring a mathematical freak, we have Champions League football next season.
“At the start of the season, well into this season we were well in the title race, but we let ourselves down, we will take positives of a trophy and semi-final of the Champions League, which was history for our club and we have Champions League next year and we have to take that.
“I have enjoyed our time under Manuel, it was important we finished off a good three years working with him.”
The stats you need to know
Manchester City have won six, drawn two and lost none of the last eight Premier League clashes with Swansea.
They have won only one of their seven final day Premier League games that they have played away from home (D3 L3).
Andre Ayew (4) has scored as many goals in his last three Premier League games as he did in his previous 23 combined.
Seven goals was the least Celtic deserved. In truth, had they scored 14 then Motherwell could scarcely have raised an objection.
If there was any doubt as to what kind of performance Celtic could find on Deila’s last day then it was answered early and emphatically.
Even before they opened the scoring midway through the first half, they created a long series of decent chances.
Rogic went close on three different occasions, Christie had two opportunities and Lustig one.
From the get-go, Celtic had a dynamism about them that Motherwell couldn’t even get close to living with.
Sure, it was a match with nothing at stake, but there was a tempo and an accuracy about their game that was exhilarating.
In the absence of midfielders Scott Brown and Nir Bitton, they had the brake off and they were relentless.
The rout was started by Tierney, a fitting flourish in a terrific breakthrough season for the teenage left-back. He cut in from the left and beat Conor Ripley at his near post.
Five minutes later, Rogic made it two and this one had a lot to do with the excellent Armstrong, who, after playing a one-two with Christie, hit a post with his shot. Rogic was on hand to tap in the loose ball.
The home fans had barely retaken their seats when it was three. An Armstrong corner was missed by the flapping Ripley and was headed home at the back post by Lustig.
Motherwell knew what was coming next – waves and waves of green and white. When they had the ball, they couldn’t keep it. When they didn’t have it, they didn’t have a clue how to get it.
They were utterly bamboozled by Celtic’s energy and should have been four behind before the break when Ripley tipped a Rogic shot into Christie’s air-space. The former Inverness Caledonian Thistle youngster had to score but put it over, much to his embarrassment.
Not that it mattered because Celtic continued the deconstruction just after the break, Armstrong teeing himself up with a nice first touch and an even nicer second one, a delicious hit into Ripley’s top corner.
Celtic Park lapped up this ruthless version of a team they have seen toil too often this season – a fast-moving, creative force that refused to ease Motherwell’s torture.
The visitors were like sitting ducks. This was a feeble and mortifying end to their season.
The fifth came quickly, Armstrong’s good work starting it and Roberts’ curling finish ending it. Motherwell backed off him and duly got what they deserved.
Four minutes later, the sixth arrived, Rogic playing Christie through and this time he made no mistake, drilling his shot past the hopelessly isolated, and totally befuddled, Ripley.
The great feel-good goal was the last one, though. Aitchison, born in 2000, slammed home his first shot on goal in senior football, a strike that will live forever in his memory no matter how many he goes on to score at this level.
For Deila, it was the perfect send-off. As the supporters of his soon-to-be former club celebrated the title into the night, the manager would be on a flight out of Glasgow, back to Norway, back to the life he had before he entered the mad world of Scottish football.
After this rout, he would have left with a smile. A bittersweet one for sure.