Bournemouth defender Nathan Ake scored a stoppage time winner to break nine-man Tottenham's resistance and earn a 1-0 victory on Saturday.
Mauricio Pochettino's men came into the match knowing three points would confirm their place in next season's Champions League -- and Lucas Moura came close to opening the scoring early on when his long-range effort almost caught rookie goalkeeper Mark Travers out of position, only to drift narrowly wide.
However, Travers then produced a succession of impressive saves to keep the visitors at bay before Spurs' game plan began to unravel.
Eric Dier was lucky not to pick up a second yellow card when he stopped a Bournemouth breakaway on 34 minutes only to see referee Craig Pawson wave play on.
And minutes later he almost gave away a penalty when he kicked Callum Wilson in the back of the leg but again Pawson said no.
Yet there was no escape for Son on 43 minutes when he was sent off for striking Jefferson Lerma in the face following a tussle with the Colombia international.
Pochettino wrung the changes at half-time as he withdrew Dier and Toby Alderweireld for Victor Wanyama and Foyth -- only to see the Argentina international dismissed two minutes and 13 seconds into the second half for a reckless tackle.
Bournemouth failed to create an openings for the majority of the game, before Ake scored a free header from a corner in stoppage time to secure all three points.
Tottenham will still be guaranteed a top four finish if Arsenal fail to beat Brighton at the Emirates on Sunday but a win for Chelsea against Watford would see them drop to fourth. Bournemouth move up to 12th.