Rey Mysterio & the Late Eddie Guerrero and John Cena & Shawn Michaels
@ Wrestlemania 21 Rey Mysterio & the late Eddie Guerrero were the SD! World Tag Team Champions, however, the WWE thought that they could have the co-holders of the SD! World Tag Team Titles go 1 on 1 and they did, and @ the end, it was Rey Mysterio who got the victory over Eddie Guerrero and after the match, the 2 of them shook hands showing tremendous sportsmanship.
2 years later @ Wrestlemania 23, John Cena & HBK were the WWE World Tag Team Champions and they also went 1 on 1.
This time, for the WWE Heavyweight Championship!
and @ the end, it was HBK who tapped out to Cena's STFU that gave him not only the win, but also, allowing him to retain the WWE Heavyweight Championship.
However, the following night on RAW in Detroit, MI
during a Tag Team Battle Royal Part 2, HBK eliminated his own Tag Team Partner, allowing The Hardys to become not only the 6x WWE World Tag Team Champions, but also the 7x World Tag Team Champions when you count WCW.
and that's a look @ the History of the World Tag Team Champions going one on one @ Wrestlemania!
credit: wrestlemania.com and geocities.com