Ronny Deila left the double-act on the bench, but introduced them after the interval when they replaced Stuart Armstrong and Scott Allan.
Commons headed in the equaliser in the 75th minute within moments of coming on.
Strachan said: “At the beginning, the better players were on the substitutes’ bench, as far as I was concerned.
“Subs can change games and that’s what happened.
“The guys who started worked hard and got the shape of the team. But they needed that bit of class and Forrest and Commons have that.”
The Scotland boss also applauded the contribution of Swedish defender Mikael Lustig.
He said: “Lustig was the best attacking player in terms of getting into areas where he can be dangerous and delivering the ball.
“That’s the hard bit, delivering while under pressure. His cross for the goal was good and it was a fantastic header from Commons because he still had a lot to do.”
The ex-Celtic manager also believed Deila can take a lot of positives despite finishing rock-bottom of Europa League Group A with only three points from six games and without a win.
He added: “I think they took something from the game. There was a nice bit of shape, they were comfortable in the first-half – then the goal goes and that’s a bit of problem.
“However, Mikael Lustig and Callum McGregor linking up on the one side was good.
“I thought Nir Bitton was good, too. Apart from a couple of passes, he looks as though he can play at this level.
“So, a lot of things went right for Celtic on the night.”
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