However, Lennon said afterwards: "There is still a lot to play for in the tie as far as I am concerned.
"I don't think it's over although our home record is very, very good.
"There was enough there to worry me as Helsingborg were very impressive.
"But in the end we hit the bar twice and, on the counter-attack, we could have put the tie well out of sight.
"We'll set the team up differently and I'd like to think we would be in the ascendancy in the home game.
"It's a great result for us to take into the second game.
"A clean sheet and two away goals was more than I could have asked for really."
Lennon rated the result as one of the best in his managerial career.
He said: "It's one of them. It's up there. But there is still a lot of work to do and 90 minutes still to go.
"There are a few bumps and bruises in there so we might have a casualty count in the morning.
"It's been a really hectic schedule for the players so their efforts tonight are even more remarkable.
"They are pretty grounded boys and they know they still have a big night ahead of them.
"But there's a big prize at the end it for them and you can see what it means for them.
"We might have to weather a bit of a storm at times in the second leg but I'm certain we will have more possession in the home leg than we did tonight."
Lennon felt Forster showed just why he was so keen to sign him on a permanent contract this northern summer after two loan spells from Newcastle United.
The Northern Irishman said: "Obviously we got off to a dream start which isn't like us because normally we're a goal down after two or three minutes away in
"So it was a great start but we took our foot off the pedal a little bit and we had to rely on Fraser making a couple of great saves.
"You can see why we pursued him so vigorously because we feel he is capable of doing that.
"We gathered ourselves at half-time and we were a lot better in the second half with
Helsingborg coach Age Hareide was defiant in defeat, claiming, contrary to what Lennon said, that Celtic will believe it is already through to the group stages.
The former Norway boss said: "It is possible (to recover) because I think Celtic will think it is over, that they are ready for the group stages and that is a good thing for us.
"Even if they say they are not, in their minds they will be thinking it is enough and they won't lose 2-0 at home.
"If it was 3-0 it would have been over but not 2-0
"One goal will make them nervous. Celtic looked disturbed and nervous in the first-half and gave us some chances.
"The same players will probably play in the second leg so we will get the chances there as well.
"We have to go for the first goal and if we get it we will have a chance.
"The minds of the players will change quickly, the pressure is still on Celtic."
Hareide knows his side paid dearly for giving away an early goal and then missing several chances to level before Samaras grabbed the second.
He said: "The last home game we scored seven and we should have scored three today.
"You get punished if you don't score goals, goals change games.
"We will need to do better when we get chances, at this level you have to put them away.
"If you don't do that then you have no chance.
"And we shouldn't have given a goal away after two minutes, that was terrible for us."
UEFA Champions League
Franck Ribery said he was happy for the whole club after helping Bayern Munich to win the UEFA Champions League.