The former England captain reprised his partnership on the right flank with defender Neville that worked so well for club and country, although United lost 2-1 to Juventus.
Manuel Giandonato and Simone Pepe scored for the Serie A side after Wayne Rooney's opener for the Premier League champions, who didn't lose at home all season.
Beckham left Alex Ferguson's United in 2003 to join Real Madrid, having graduated with Neville into the first team after winning the 1992 FA Youth Cup.
They both received the loudest cheers at Old Trafford, where in one late moment of drama Beckham helped to restrain a fan who invaded the pitch.
Beckham and Neville were also reunited with other members of the so-called "Fergie's Fledglings," with Nicky Butt, who is now at Newcastle, Gary Neville's brother Phil, who now captains Everton, Paul Scholes and Ryan Giggs.
Neville left the pitch to a standing ovation after 83 minutes, embracing Beckham and drawing a close to a United career that saw him play 602 first-team games for his boyhood club.
Neville won the Champions League, eight Premier League titles, three FA Cups, two League Cup titles, the Intercontinental Cup and the Club World Cup along the way.