United's new perch was achieved courtesy of a second consecutive 2-0 win over Otelul Galati, and rivals Benfica dropping two points at home to Basel. Now the Reds boss is buzzing at the prospect of hosting the Portuguese side on 22 November, with a chance to go through to the knock-out stages as group winners.
"It's down to us," said Sir Alex. "If we beat Benfica, we've won the group, simply that. It's a good incentive for us, being at home on a big night. Manchester United and Benfica... the history between the two clubs is fantastic, so hopefully it will be a very, very good night."
Just as they did a fortnight ago in their native Romania, Otelul Galati earned Sir Alex's praise with their tenacious approach to the game - and the way they kept the floodgates closed, even after conceding an 8th-minute goal to Antonio Valencia.
"The winning was important tonight," stressed the United manager. "Our opponents were aggressive, defended very well, pressed the ball everywhere on the pitch, put some energy into their game and made it difficult for us."
The Reds had to wait until the 87th minute to seal the victory, with a shot from striker-turned-midfielder Wayne Rooney - rated as the best player on the night by his boss.
"I thought he was fantastic in central midfield, I really did," praised Sir Alex. "His awareness of people around him, his choice of passing was very, very good. He did really well for us tonight. It's difficult to say how Wayne would play in another Champions League game but I'd be confident playing him there."