Korea Repbulic midfielder Kim Bo-kyung's dramatic stoppage-time equaliser earned Cardiff City a 2-2 draw that prevented Manchester United from climbing into the English Premier League's top four on Sunday.
United were on course for the UEFA Champions League places until Kim stole in to head home a Peter Whittingham free-kick in the 91st minute.
Surprise 3-2 victors over Manchester City earlier in the season, Cardiff inched three points clear of the bottom three thanks to Kim's goal, while United were left in sixth place, seven points behind leaders Arsenal.
Wayne Rooney started the scoring, who put United ahead in the 15th minute.
Antonio Valencia's right-wing centre was flicked on by Javier Hernandez to Rooney, who turned inside and let fly with a shot that beat goalkeeper David Marshall via a deflection off Gary Medel.
Cardiff's supporters saw their side draw level in the 33rd minute with a beautifully constructed goal.
Medel found Whittingham, who helped the ball on to Mutch, and the recipient of the kick from Rooney released former United striker Fraizer Campbell to beat goalkeeper David de Gea with a first-time finish.
The hosts' joy was short lived, however, as Patrice Evra restored the champions' lead on the stroke of half-time when he headed home from Rooney's left-wing corner.
In response, Campbell saw a feathery chip come back off the bar, but United looked to have escaped until they gave away one free-kick too many and Kim dispatched Whittingham's centre to send the stadium into raptures.
For United, extending their unbeaten run to ten games provided scant consolation, particularly as Kim's goal prevented them from supplanting Manchester City in the top four.
City put six past Spurs
Beaten 1-0 by Sunderland in their last outing prior to the international break, City did not look back after Jesus Navas gave them the lead after only 14 seconds for the fastest-ever Premier League goal.
Aguero claimed a brace either side of half-time, tucking away centres from Navas and Yaya Toure, to take his tally of goals to 14 in his last 11 appearances. Alvaro Negredo added a fifth in the 55th minute, flummoxing Michael Dawson with an audacious turn and lashing a left-foot shot past Lloris, before Navas completed the rout in injury time.
"It is impossible to play better than today. We are working to have one style of playing and to continue in the same way," said City manager Manuel Pellegrini.
"We're thinking just about each game. Now we play in the Champions League on Wednesday (against Viktoria Pilsen) and after we see what happens with other teams, how many points they drop, and I'm absolutely sure we will also win matches away."
Victory preserved City's 100 per cent home record in the league this season and having annihilated Norwich City 7-0 in their last fixture at the Etihad, they have now scored 13 goals in their last two home games.
Pellegrini's side moved above Southampton into the top four, six points below leaders Arsenal, while Spurs slipped to ninth place. Andre Villas-Boas's men had only conceded six goals all season prior to their trip to Manchester and although they are only two points below City, they have now gone three games without victory.
"Everything went wrong for us, every opportunity was a goal and we paid a heavy price - too much for what we deserved," said Villas-Boas. "City were excellent, and we were extremely poor. We have to be ashamed of ourselves, and react to a defeat like this."