5 hard fights in a row.

[ICB]

Antonio Margarito's last few opponents have been top quality except for Golden Johnson.

Joshua Clottey
Paul Williams
Golden Johnson
Kermit Cintron
Miguel Cotto

Or how about Juan Manuel Marquez

Jimrex Jaca
MAB
Rocky Juarez
Manny Pacquiao
Joel Casamayor

To be honest i think Marquez takes this one that is a pretty impressive list of fighters, and especially since all of those fights were tough except for maybe the Juarez fight, but the fight still went 12 rounds and although he outboxed Juarez. He had to work hard in some parts of the fight.