The 26-year-old injured his ankle in Celtic’s Scottish Cup victory three months ago which forced him to miss Australia’s World Cup qualifier against Kuwait on September 10.
“He is in the best best condition I have seen, the definition in his body and work rate away from the games has been fantastic and he is a real asset when he is fit and firing.
“It was a wonderful goal as well.”
Ivorian striker Vakoun Issouf Bayo, one of eight changes made by Lennon on Wednesday night, opened the scoring for the defending champions in the 15th minute.
After the break fans were still returning to their seats when Bayo took a pass from Olivier Ntcham and set up Rogic, who sidefooted the ball into the net from 16 yards.
Rogic peppered Thistle’s goal but strikes from fellow midfielder Ntcham (56th, 63rd) and substitute Scott Sinclair (76th) secured a comfortable win.
Meanwhile, Celtic and Rangers avoided each other when the semi-final draw was done.
Celtic were rewarded for their big win with a last-four tie against Hibernian, who drew 0-0 at Kilmarnock before winning 5-4 on penalties.
Old Firm rivals Rangers, who beat Livingston 1-0, will take on Hearts who saw off Aberdeen 3-0 in another shootout after a 2-2 draw.