Chelsea and Tottenham Hotspur's hopes of qualifying for next season's Champions League remain in the balance after a thrilling draw at Stamford Bridge.
Oscar put the hosts ahead after 10 minutes as he reacted first to Gary Cahill's header, but Emmanuel Adebayor's beautifully flighted effort drew Spurs level.
Ramires swept home to reestablished Chelsea's lead before the break, which looked to have all but secured top-level European football for next term, but Tottenham equalised for a second time after substitute Gylfi Sigurdson drove past Petr Cech.
The result keeps both sides' ambitions alive of qualifying for the Champions League, with The Blues three points clear of fifth place Spurs, who cut the gap to Arsenal in fourth to just one point with two games remaining.
Andre Villas-Boas, returning to Chelsea for the first time since his sacking last March, was seeking to end a 23-year wait for a Spurs win in west London and give their hopes of finishing in the Premier League top four a shot in the arm.
Such was Chelsea's superior goal difference and three point lead over Tottenham in the table, victory would put them on the brink of a top four finish and they went someway to securing that status as Oscar netted his fourth league of the season as the Brazilian escaped the attention of Scott Parker and nodded home following Cahill's header.
Despite the home side's dominance in possession it was the visitors who drew level as Adebayor picked the ball up deep inside his own half and took advantage of a hesitant Chelsea back-four, without captain John Terry, and curled beyond a motionless Cech into the top corner from 25 yards.
But before the interval Chelsea hit the front for a second time as Fernando Torres exposed Jan Vertonghen's poor positioning and fed the onrushing Ramires, who smashed into the corner despite being off-balance.
The introduction of Clint Dempsey and Sigurdsson sought to swing the game back in the away side's favour, and having survived Ramires' slip after being played in by Mata, Spurs got what could prove to be a crucial leveler on 80 minutes.
Beniot Assou-Ekotto's innocuous cross into Adebayor saw the Togo international flick the ball into the path of Sigurdsson, who rifled into the corner.
Gareth Bale, who remained on the peripheral on much of the evening, almost grabbed all three points for the north Londoners but his free-kick went straight at Cech as the points were shared with the pair's European hopes set to go to the final two weekends of the season.