Sloppy defending allowed Pantelis Kapetanos to sweep the Romanian champions into the lead, but the Reds refused to panic and took the spoils through Robin van Persie's brace.
In closing out the victory and demonstrating the calm possession play so glaringly absent in last term's ill-fated campaign, the players impressed their manager.
"I've got to be pleased with the possession and the concentration was really good tonight," Sir Alex told ITV Sport. "Apart from the goal we defended very well. They hit so many really good, telling crosses into our box that kept us under pressure all the time, kept us on edge.
"David (De Gea) made a good save at the end so I've got to be pleased. Coming away from home in Europe is never easy and as I said before the game, they've a good record here."
The boss also took time to salute the work of both match-winner van Persie and Wayne Rooney, whose sublime assist teed up the Dutchman's winning goal.
"The pass and the finish were both equally as good," he said. "Fantastic finish of course, but what a nice ball Wayne has dropped in. I thought actually it was too far, but Robin did well to get to it."