James Forrest and Biram Kayal scored the goals which beat Ajax 2-1 at Parkhead and the teams now meet again in Amsterdam on November 6. Barcelona have seven points, AC Milan four, Celtic three and Ajax one. Celtic's campaign would have been effectively over if they had lost but they dug out a priceless win after back-to-back defeats against the group's top two.
"It leaves us in a very good position," said Lennon. "We'll have to get a good result at Ajax if we can and on tonight's evidence that's going to be very difficult. But it's not beyond us. This win gives us three points, we're only two points behind Milan now. So this is a massive win in the context of the group.
"I knew the group was going to be tight and difficult. If we had lost tonight we would be sitting with no points from three games. We would have been out, we'd have been chasing our tails, but we have given ourselves a great chance now. We're going to have to play well in Amsterdam to get something out of the game but I feel we are capable of doing that. If we had got a draw tonight it wouldn't have been the end of the world but we got the win so it's wide open again.
"I thought we looked a little bit anxious at times. But then this is Champions League football and Ajax are an excellent side. I did say going into the game that they would give us as many problems as Barcelona and Milan and that proved to be the case. But as the second half wore on we got better and better and I thought we thoroughly deserved to win."
Forrest was coolness personified as he buried the first-half penalty which put Celtic ahead. He told Lennon yesterday he had never missed one. "We decided he'd step up and take it because obviously Kris was out. There was a lot of gamesmanship going on with their keeper but James kept his cool. It was a big moment."
Kayal's second-half drive was deflected in for 2-0. "I thought Biram was worth his weight in gold," said Lennon. "He can be very proud of his performance, we're delighted with that. He's been a little bit flat since his heavy injury but that was more like him tonight. I also thought Emilio Izaguirre was fantastic as was Georgios Samaras again. Forrest got better as the game went on and the stalwarts in the team - Efe Ambrose, Mikael Lustig, Virgil van Dijk, Charlie Mulgrew - are turning into some group of players."
Lennon had "no complaints" about Nir Biton's late red card for a crude challenge on Thulani Sereno. "He left the trailing leg high. Although if he had been playing on Saturday at Easter Road he'd probably have only got a booking for that."
Lustig was replaced near the end because of a recurrence of a hip problem and is a doubt for Sunday's game at Partick Thistle.
Ajax scored with almost the game's final kick. Manager Frank de Boer felt his young team deserved more: "Celtic didn't create anything although they scored twice. We dominated the game but only scored one goal. I am disappointed but comfortable about the way we played. Eight times out of 10 the best team wins. We were the best team tonight but goals win games."