Report: United 1 Roma 0
There was no repeat of April's Roman demolition but United did enough to take all three points against an Italian side desperate to avenge last season's embarrassing defeat.
The Reds dominated for large spells but couldn't force the ball in during the first half. In the end, it was Wayne Rooney who broke the deadlock with a predatory strike in the 70th minute to hand Sir Alex yet another European scalp.
The United boss opted for pace down the flanks in his team selection, picking both Cristiano Ronaldo and Nani at the expense of the experienced Ryan Giggs.
Louis Saha was handed his first start since February, while John O'Shea slotted in at right back for the injured Wes Brown. There was no Owen Hargreaves in the squad, although Nemanja Vidic passed a late fitness test to take his spot in the centre of defence alongside Rio Ferdinand.
In goal, Tomasz Kuszczak made his European debut and he had to be alert as early as the 10th minute when Francesco Totti fired a long-range effort straight at the Pole. It did little to trouble Kuszczak but suggested last season's European Golden Boot winner had once again adopted the shoot-on-sight policy we saw here at Old Trafford in April.
Of course, on that occasion, United went 3-0 up before 20 minutes. Tonight, the pace was less frenetic in the opening exchanges, as the new-look Roma back four stood firm against United's two-pronged strikeforce of Rooney and Saha.
Nani unwittingly came close on 17 minutes when he stretched to keep a Rio Ferdinand pass in play and the ball cannoned off his shin and across the six-yard box.
Two minutes later, the Portuguese winger earned a free kick when Lancashire-born Simone Perrotta caught him 25 yards from goal. Ronaldo lined up the ball but blasted the set-piece into the Italian wall.
It began a period of real dominance for the Reds, with Nani and Ronaldo again involved moments later. United had a half-hearted penalty appeal for handball turned down after a Nani pass struck a Roma defender on the arm. But there was more concern for the Italians in the next phase of play, as Nani whipped in a curling cross that Ronaldo narrowly directed over the bar from six yards.
The summer signing from Sporting Lisbon went close himself on 27 minutes when an in-swinging cross from the left-wing forced goalkeeper Curci to athletically tip the ball clear. Louis Saha then stung Curci's palms before a Totti free kick kept Kuszczak alert at the other end.
But it was all United and once again it was Nani who fashioned a chance for the Reds. This time he beat De Rossi on the left before curling a ball to the back post where Wayne Rooney volleyed over from close range.
Curci required treatment shortly afterwards when he collided with Saha at a United corner but the Italian stopper recovered sufficiently to continue and ensure Roma went to the break on level terms. He'd certainly been the busier goalkeeper, although Roma manager Luciano Spalletti would have been pleased to go into the dressing room at 0-0.
Sir Alex told ITV during the break he expected the Reds to take a few more risks in the second half and Ronaldo fired a low cross into the box early on. But it was Francesco Totti who perhaps should have put the visitors ahead in the 48th minute. Nemanja Vidic slipped in the penalty area, allowing Totti space. With Kuszczak bearing down on the striker, Totti was forced to take the chance early but could only clip the ball over both goalkeeper and crossbar.
It was a lively start to the second period and Nani almost illuminated the match further when his cross-come-shot brushed the top of the Roma crossbar after he'd carved open the Italian defence on the edge of the penalty area.
Wayne Rooney forced a smart save from Curci at his near post on 65 minutes before Cristiano Ronaldo found the net on 69 minutes with a cheeky backheel. To the Reds' dismay, the Portuguese winger was ruled offside and he was denied a second European goal in as many games.
There was no doubting the validity of Wayne Rooney's strike a minute later. The England international latched onto Nani's clever pass to fire a first-time drive across Curci and in off the far post to send United ahead. It was Rooney's first goal of the season and no more than he deserved after a night of tireless running and clever interchange play.
Carlos Tevez almost made it 2-0 when he flashed a shot inches wide from long range before Rio Ferdinand blocked a Ludovic Giuly shot that may well have been heading into the far corner.
But Roma's best chances were still to come, with Max Tonetto miscuing a volley at the back post in the 82nd minute before substitute Ahmed Esposito blasted wide with the goal at his mercy and just three minutes on the clock. That opportunity arrived with the Reds down to 10 men, after Ronaldo, bloodied and groggy from a Mirko Vucinic elbow, had disappeared down the tunnel a minute earlier to receive four stitches.
Even with a numerical disadvantage, Sir Alex's men hung on for a memorable win… even if it didn't arrive in quite the same fashion as April's epic 7-1.
Attendance: 73, 652
United: Kuszczak; O'Shea, Vidic, Ferdinand, Evra; Carrick, Scholes, Ronaldo, Nani (Giggs 80); Rooney (Anderson 85), Saha (Tevez 66)
Subs not used: Heaton, Pique, Simpson, Eagles
AS Roma: Curci; Cicinho, Juan, Mexes, Tonetto; De Rossi, Aquilani (Pizarro 61), Giuly (Esposito 80), Perrotta, Mancini (Vucinic 74); Totti
Subs not used: Sergio, Antunes, Barusso, Brighi