Forster kept an invaluable clean sheet, despite Celtic being on the back foot for long periods, as they snatched a 2-0 win away to Swedish champions Helsingborg in the first leg of their qualifying play-off.
Kris Commons’ well-struck volley after two minutes gave the Hoops an early advantage they clung on to, thanks largely to Forster, before Georgios Samaras doubled their lead with 15 minutes left.
Despite the value of those strikes Lennon was full of praise for his goalkeeper Forster.
“Fraser’s done his chances [of an England call-up] no harm tonight,” Lennon said. “I thought he was excellent.”
Lennon admitted his side had been flattered by a scoreline that leaves them in pole position to progress ahead of the return leg at Celtic Park next week.
“We had to rely on our goalkeeper. That’s what you have to do away from home,” he said.
“The second half we were a lot better; we had to change the shape of the team.
“The job is only half done. There is a big game at Celtic Park to come. Helsingborg showed how dangerous they can be.”
Lennon’s side might have rode their luck at times but they could have won by more in the end and now face the tantalising prospect of mixing with the elite clubs in Europe for the first time since the 2008/09 season.
Celtic stormed into an early lead. Samaras picked up a pass from Joe Ledley on the left and, when his cross came into the middle, the unmarked Commons slammed it past the helpless Par Hansson from 12 yards.
The Parkhead side were fortunate to have their lead intact by the time the interval whistle sounded after a series of close calls.
Winger James Forrest replaced Kayal for the start of the second half, with Commons moving into the middle to support Gary Hooper.
After Ledley picked up an injury and was replaced by Kelvin Wilson, Helsingborg substitute David Accam ballooned the ball over the bar from 14 yards.
Celtic’s sucker punch came when Commons’ corner from the right was met by Samaras at the back post and he headed past Hansson from a couple of yards to double the visitors’ lead.
The goal knocked the stuffing out of Helsingborg, who should have been dead and buried three minutes later when Samaras ran through on goal but the Greece striker curled his right-footed shot wide of the far post.
HELSINGBORGS IF: Hansson, Atta, Christoffer Andersson, Wahlstedt (Accam 63), Uronen, Sadiku, Mahlangu, Gashi, Bedoya, Sorum (Dos Santos 65), Djurdjic.
CELTIC: Forster, Matthews, Izaguirre, Mulgrew, Rogne, Brown, Commons (Watt 89), Ledley (Wilson 65), Kayal (Forrest 46), Samaras, Hooper.
Referee: O Benquerenca (Portugal).