Manchester United breathed new life into their flickering title defense with a 1-0 win today over top of the table Arsenal . A header by Arsenal's former captain, Robin van Persie, off service from man of the match Wayne Rooney, was enough to secure the win and move United to within five points of first place.

It seemed like the old days, with United downing Arsenal at home, as they have now done 15 times out of the 23 games the Gunners have played here under Wenger. But this is not those old, confident days, so make no mistake: for United this was a major win. United started the weekend staring at the possibility of slipping eleven points off the top, a margin that would have almost surely ended their hopes of a title defense. Facing a must-win, United put together a disciplined performance that kept the Gunners entirely at bay, limited mainly to pot-shots from range.

It was the kind of ugly and gritty win the Red Devils were once well known for, but that quality has been sorely lacking this season under new manager David Moyes. Fittingly enough, no man celebrated more at the final whistle than United's old manager, Sir Alex Ferguson, who was observing the match from the director's box above. Some would argue the gaffer's shadow hangs too heavily over this team. That may be the case, but there's something to be said for the way they channeled his old style today.

"We knew we couldn't afford to lose today," said Rooney after the game. "And with the other results today, we knew a victory would put us right back into it. I think this was the toughest we've been to play [against] and to break down. It was a great effort from everyone."

Manchester United's pressing game kept Arsenal strangled for the better part of an hour, unable to create any width and marginalizing key man Bacary Sagna until quite late. Phil Jones and Chris Smalling spurred the attack from deep-lying positions, allowing Rooney to maraud right down the gut at Arsenal's net. With Mikel Arteta and Mathieu Flamini forced to play as effective defenders, this kept Aaron Ramsey from fully turning over. Olivier Giroud looked brighter than he has in the past few games, but starved for support up top, he was unable to seriously trouble David De Gea in the net.

When the goal came, it must have inspired flashbacks among Arsenal fans to the bad old days of last season: it was off a set-piece, and it was a case of the Gunners' zonal marking collapsing. Van Persie was allowed to run onto Rooney's corner, where he out jumped Giroud to head home at the post. Giroud lost his man, but more damaging was the gap left by Kieran Gibbs on the post: Had he held his position, he might have kept the ball out. Van Persie earned the ire of the away fans with his wild celebrations afterward, and they were certainly in questionable taste given his long history with Arsenal.

Wayne Rooney provided the delivery, Robin van Persie the header. (Photo: Tom Purslow/Getty Images)

But given van Persie's gyrating was the biggest talking point in this match to that point is also an illustration of how lacking in entertainment the game truly was. For this was not the firecracker we had all hoped for, just predictable: Old Trafford has been a theater of nightmares for the Gunners. And while Arsenal will look back at this week with some pride - they passed major tests against Liverpool and Dortmund - this was a missed opportunity that exposed a key weakness in their squad.

Per Mertesacker and Tomas Rosicky were both out due to a virus that swept through the Arsenal camp the night before. While Arsene Wenger took pains pre-game to point out that this was "not an excuse," the truth is both were badly missed. The bigger picture is that Arsenal's lack of depth, particularly up top, continues to call into question their long-term viability as a contender. There is no question they have the skill and the class; there are serious questions over whether or not they have the bodies.

"Our heart was there, our desire was there today - maybe too much," said a chastened Wenger after the match. "I felt we were too nervous in the first half, and lost too many balls. When we came out in the second half, we played a more efficient game and we were very close, very, very close many times. But now, we have to digest this and come back after the break in a strong way."

This is not a Waterloo for Arsenal any more than it is a harbinger of things to come for United. Both teams have flaws, and either team can win - or lose - on a given day. But today was a reminder, not only of how much pride United have and how hard they can be to beat, but of the distance Arsenal still have to go to be champions this season. Both teams will go into the break with questions to answer, and both will go in January with needs to address. How they answer those questions could well decide their seasons.

NOTES: Nemanja Vidic and Wojciech Szczesny were both involved in bad clashes that saw ref Michael Oliver stop play under the sport's head injury protocol. Szczesny would continue; Vidic was taken to hospital and David Moyes said after the game that "it looked a bad one."