The Scot and the Irishman, of course, helped to form the backbone of the great Hoops team that Martin O'Neill managed a decade ago. But at Carrow Road last night, in the testimonial match for Norwich stalwart Adam Drury, the former team-mates found themselves on opposing sides.
Lambert, now one of the hottest properties in management in England as a result of his fine achievements with the Canaries, was in his usual place in the home dugout.
Across from him in the visitors' technical area, his old friend Lennon took charge of his first match since his team's title-winning season ended.
The nature of the friendly, which came nine days after Scott Brown lifted aloft the SPL trophy at Parkhead, meant the 2-0 win for the hosts was virtually meaningless. Norwich fans came to pay tribute to a defender who has given 11 years of dedicated service, through good and bad, to the Norfolk club.
The Barclays Premier League outfit's current players, fresh from finishing a highly respectable 12th in their first season back in the top flight, turned out in force. And a few stars of old, ex-Celt Dion Dublin, Darren Huckerby, Michael Nelson, Dani Pacheco and Henri Lansbury, all showed up as a mark of respect to their former comrade.
Lennon, meanwhile, used the game to give a host of the promising youngsters fast emerging from the Lennoxtown training complex a taste of top-team experience.
First-team regulars Kris Commons, Gary Hooper, Fraser Forster, Paddy McCourt, Anthony Stokes and Kelvin Wilson all started their club's first meeting with Norwich since 2001. Yet, they were joined in the starting XI by Stuart Findlay, Dylan McGeouch and Tony Watt.
Lewis Kidd, Jamie Lindsay, Paddy McNally, Bobby Thomson and Denny Johnston all made their first appearances when they replaced Rabiu Ibrahim, Stokes, Andre Blackman, Forster and Hooper in the second half.
In addition, Ibrahim and Blackman, two players hopeful of featuring on a far more regular basis in Lennon's team in the 2012/13 campaign than they have to date, also kicked off the outing.
Nevertheless, the match highlighted the huge strides both Lambert and Lennon have made in management since they last played together in a competitive fixture for Celtic back in 2005.
Lambert's team has won back-to-back promotions from League One and the Championship and more than held its own alongside giants like Arsenal, Manchester United and Spurs in the last nine months.
The Champions League winner, who cut his teeth in management at Livingston, Wycombe and Colchester, is being linked with the vacant positions at Aston Villa and, by some, Liverpool.
Lennon, meanwhile, will spend much of the close season putting together a squad capable of returning to the Champions League group stage he enjoyed so many great nights playing in.
It is still early days in their managerial careers, but both men have shown enough on vastly differing stages to suggest they will be just as successful as they were as players.
The bright displays of their respective teams on a balmy evening in Norwich at such a late stage in the season – the game was a full 11 months after Celtic played their first pre-season friendly – were a credit to them.
Making his debut at centre-half alongside Wilson against such accomplished opposition was a tall order for teenage defender Findlay. He was up against James Vaughan.
The 16-year-old was perhaps at fault for the home team's opening goal. Jonny Howson sent Wes Hoolahan clear down the left flank and he cut the ball back to Vaughan in space in the penalty box who buried the ball between the legs of Forster.
However, that lapse in concentration aside, Findlay showed up well. He looked composed on the ball, distributed it intelligently and did well in the air. He will, like his contemporaries, learn from the experience.
Watt, who great things have been predicted of since he netted two goals on his debut against Motherwell at Fir Park earlier this season, posed Celtic's greatest goal threat despite playing wide. He tested Jed Steer with powerful left-footed shots in both halves.
Substitute Lansbury put the hosts two goals ahead in 69 minutes after a poor clearance by keeper Forster – who spent a season on loan at Norwich before joining Celtic – went straight to Pacheco.
The Celtic fans were, unsurprisingly given the location of the match in the south-east of England, greatly outnumbered, but they outsang their counterparts and drew a round of applause for their mass huddle.
Norwich boss Lambert said: "Neil was more than happy to bring his team down and I would like to thank him for it. It was a mark of the man. Getting Celtic to come and play us was special. It was a great atmosphere."
CELTIC: Forster (Thompson 87), McGeouch, Wilson, Findlay, Blackman (McNally 80), Ibrahim (Kidd 67), Commons, McCourt, Watt, Hooper (Johnston 87), Stokes (Lindsay 76).