Deep in injury time, with a header every bit as emphatic as his overall performance had been insipid, Thierry Henry taught Manchester United a valuable lesson in taking nothing for granted.

Anonymous for 92 minutes, the Arsenal captain was feted for his nonchalant glance in the 93rd.

Just seven minutes shy of leaving north London with a nine-point lead in the Premiership, after Chelsea's charitable display at Anfield on Saturday and Wayne Rooney's first goal in six weeks, United came inexplicably unstuck.

Identical crosses from Arsenal's right caught Sir Alex Ferguson's title contenders cold.

Instead of embarking on a celebratory circuit of the Emirates Stadium, their first title in four years all but in the bag, United had to contend with an enigmatic Arsene Wenger thumping the air in satisfaction and Henry and Emmanuel Adebayor doing a curious dance on the touchline.

Arsenal's first home win over United since November 2001, it was also a rare double over a side that started the eagerly anticipated contest with such pace and conviction, Jose Mourinho might have been inclined to change channels.

He had promised to take the kids out for treat, but surely the Chelsea manager was watching yesterday's drama unfold, so fascinating was the duel between two of the season's most compulsive entertainers. The gap remains six points, but for Chelsea, there is suddenly room for manoeuvre.

Unbeaten, if not entirely convincing, in their new home, Arsenal started as fitfully as they finished with a flourish. It was rampant, pugnacious United who showed all the flare in the opening 15 minutes, treating a record home crowd of 60,128 to a fast, fluent and lively start.

In September, United were passed off the pitch by an Arsenal XI infinitely more convincing than the 1-0 scoreline suggests. Yesterday, with Ryan Giggs and Paul Scholes restored to a five-man midfield that included Rooney on the left, it was United's turn to hog possession.

Five minutes lapsed before Mathieu Flamini, replacement for the suspended Gilberto Silva, managed to get an Arsenal toe on the ball and another three before Henry managed a touch. Such was United's total control, with Michael Carrick pulling the strings and a bevy of blue shirts dancing in attendance. Giggs, after a cushioned touch from Henrik Larsson, stroked wide. So, too, Cristiano Ronaldo.

For those under the impression this fixture has lost some of its bite with the departure of arch mixers Patrick Vieira and Roy Keane, Kolo Toure saw yellow inside 15 minutes, while Rooney and Emmanuel Eboue waged a tasty war on the left, culminating in tit-for-tat slaps and a booking for the latter.

The enigmatic Giggs, busy cutting inside, also found his way into referee Steve Bennett's black book for a tackle from behind on Cesc Fabregas. It was harsh. The veteran midfielder was simply a victim of his own energy and enthusiasm.

But as Larsson registered United's first shot on target, a strike with insufficient welly, Arsenal awoke with a start. From a congested midfield Fabregas emerged, winning his own personal battle with Scholes, while Gael Clichy, encouraged by Ronaldo's reluctance to backtrack, made hay on the left.

There then followed a period, as thrilling as it was galling for those desperate to see the deadlock broken. As is their want, pedantic Arsenal, committed to creating a thing of beauty, wasted umpteen opportunities with their elaborate gestures in front of goal.

Fabregas' effort was an exception to the rule, but his stinging strike from distance, on target and destined to test Edwin van der Sar, pole-axed the unfortunate Nemanj Vidic.

For United, Rooney threatened in the 35th minute, breaking at speed. But instead of going for the jugular, he cut inside and lost sight of the target.

However, if it was a loss of self-confidence that had persuaded the United striker to take a more indirect route, it was not apparent moments later, when Arsenal required a finger-tip save from keeper Jens Lehmann to deny Rooney in added time.

Fifteen points may have separated the two sides at kick-off but there was little between them on the pitch. Henry was rightly denied a penalty in the 37th minute, when he fell beneath an imaginary challenge from Gary Neville. So competent was Clichy, Ronaldo was forced to seek his fortune on the opposite flank.

It was a disappointing afternoon for the Portuguese youngster, but as so happens, the slack was taken up by Rooney. Ferguson had promised his young striker would find his goal-scoring touch sooner rather than later and so it proved.

Eight minutes after the restart, the jinx was broken, Patrice Evra's delightful overlap and perfectly weighted delivery from the left finding Rooney at the far post. A purposeful header, his eighth goal of the season but first since the start of December, saw the jubilant player engulfed in well-wishers.

To Arsenal's credit, they stuck to their task with Wenger providing extra muscle in attack, Julio Baptista and Robin van Persie replacing Alexander Hleb and Flamini. The new additions, combined with a more direct approach and saw swift dividends.

In the 83rd minute, the persistence of Fabregas and Rosicky was rewarded with Scholes surrendering critical possession in the United third. The latter punched over a smart cross for van Persie to bury in the roof of the net with a stunning left-foot strike at the far post.

From the same position in injury time, out on United's suspect left flank, Eboue produced the killer blow, another deft delivery that cleared Vidic's head by a margin but found the one that mattered.

It was Henry's fourth goal in as many games. The look on Ferguson's face said it all.