Manchester United's Champions League hopes were left hanging in the balance on Tuesday as Portuguese rivals Benfica snatched a 2-2 draw to reach the last 16 at Old Trafford.

Argentinian veteran Pablo Aimar punished some slack United play to secure a precious point for Benfica after United had fought back from an early Phil Jones own goal to lead through strikes from Dimitar Berbatov and Darren Fletcher.

Although the result left Benfica and United level on nine points, the Portuguese can clinch top spot in Group C if they beat Romanian whipping boys Otelul Galati in their final group game in Lisbon by virtue of their better head-to-head record with United.

United, meanwhile, face a tricky final game at Swiss side FC Basel, who can qualify for the last 16 at the expense of the Premier League giants if they manage to defeat Sir Alex Ferguson's side.

Ferguson, who had suffered a blow before kick-off when Wayne Rooney was ruled out through injury, was left ruing another frustrating result for his team.

It was the second time this season that United had led a home Champions League fixture only to let victory slip through their fingers, following their 3-3 draw with Basel.

"It was very disappointing," Ferguson said. "A bit freakish to be honest with you ... but we played so well tonight, made some good chances and played some good football.

"I've no fault with my players at all - we deserved better. It's a cruel game at times and it was cruel for us tonight."

United had got off to a disastrous start, conceding a goal after only three minutes as Benfica impressed with some enterprising early play.

Maxi Pereira and Nicolas Gaitan combined well to carve out an opening down the right flank, and when Gaitan rifled in a low shot United defender Jones stuck out a leg and turned the ball into his own net.

The goal stunned Old Trafford into silence and United looked shellshocked by the setback for several minutes afterwards.

Eventually United regained their composure and soon Nani was threatening, Ezequiel Garay earning a yellow card for an ugly tackle on the Portuguese winger in the 16th minute.

Nani was at the heart of United's equaliser on the half-hour mark. A quick free-kick was spread wide to the winger who curled in an inviting cross for Berbatov to glance beyond Artur in the Benfica goal.

It might have been 2-1 just seconds later as Ashley Young was put clean through on goal only to see his shot blocked by the advancing Artur.

A breathless passage of play continued as Benfica swept up the other end and Aimar saw his angled shot well saved by David de Gea.

An increasingly niggly game saw Fletcher become the next man to be booked for dissent before Artur picked up a further caution for time-wasting.

United were quick out of the blocks after the break, subjecting Benfica to wave after wave of attacks.

More good work from Nani created an opening for Young but the striker's shot was blocked by frantic Benfica defending on 50 minutes.

On 59 minutes Benfica's defence finally cracked. Patrice Evra curled in a teasing cross from the left flank and Fletcher timed his run superbly to prod past Artur. The Benfica goalkeeper did well to block Fletcher's shot but the Scotland captain carried on his run and smashed in from close range for 2-1.

But just as it looked as if United were poised to take control of the contest, Benfica grabbed an unlikely equaliser inside a minute.

A sloppy clearance from de Gea fell to the elusive Bruno Cesar, and the Benfica winger raced to the byline and crossed.

Cesar's centre slammed into an off-balance Rio Ferdinand and fell to Aimar who lashed high into the net for 2-2.

United pressed relentlessly over the final quarter but United's best chance for a winner was squandered by Berbatov, the Bulgarian striker volleying high over the bar from close range on 78 minutes.

It might have got worse for United on 89 minutes when Rodrigo burst into the box only to shoot into the side netting.