Celtic scored three goals in the second half as they progressed to the quarter-finals of the Scottish Cup with a 3-0 win over First Division Raith Rovers at Starks Park.
The Hoops dominated the first half but the closest they came was when Charlie Mulgrew's inswinging corner came crashing off the post.
After having a series of earlier penalty claims turned down the Hoops were finally awarded a spot-kick in the 54th minute which Commons won and expertly dispatched.
Substitute Scott Brown missed a golden chance to add another before fellow sub James Forrest made it 2-0 with a fine finish in the 83rd minute.
Charlie Mulgrew's curling 86th-minute effort sealed victory as they made sure there was no repeat of last weekend's shock League Cup exit to St Mirren.
Celtic manager Neil Lennon was delighted with his side.
"It was excellent from the first whistle. Our attitude was a lot better and overall it was a very professional performance from us," Lennon said.
"We just felt that once we got the first goal the game would open up for us and that's exactly what it did."
Raith Rovers manager Grant Murray was proud of his players.
"We created a few chances in the second half but Celtic's quality shone through.
"The boys enjoyed it and battled hard," Murray, whose side were also knocked out of the League Cup by Celtic earlier this season, said.
"We are disappointed to lose any game but we put a lot of effort into the game and we can take a lot of belief from it. It was a great challenge against a Champions League team."
The Hoops had their First Division opponents pinned in their own half from the start and were appealing for a penalty early on when Tony Watt's cross into the box appeared to hit the arm of Eddie Malone but referee Steven McLean ignored their pleas.
Raith finally managed an effort at goal on the half hour mark but Brian Graham's header was weak and didn't trouble Lukasz Zaluska.
Celtic came close to taking the lead direct from a corner when Mulgrew swung in a kick from the right and it missed everyone in a congested penalty area before clipping the far post.
Mensing had survived an earlier penalty claim when he clashed with Commons in the box but the defender wasn't so lucky in the 55th minute when referee McLean pointed to the spot after he clipped the ankles of the Scotland international just inside the box.
Commons dusted himself off to take the kick himself and planted it in the bottom right-hand corner giving McGurn no chance.
Substitute Brown spurned a glorious chance to put Celtic further ahead when McGurn could only push Gary Hooper's stinging shot into his path but the midfielder snatched at the rebound and his shot went wide from six yards out.
On his return from injury Forrest, who had replaced Watt, made it 2-0 in the 83rd minute. Forrest and Hooper exchanged passes before the winger raced into the box and clipped the ball beyond the advancing McGurn.
The Hoops made sure of their quarter-final place when Mulgrew added a third in the 85th minute. Joe Ledley teed up his team mate to curl a strike into the top right-hand corner past the helpless McGurn.