Check out Nalbandian's draw at the 2007 Madrid Masters.
2nd round - Berdych
3rd round - Del Potro
QF - Nadal
SF - Djokovic
F - Federer
If Del Potro didn't pull off an upset (remember it's 2007) and beat Robredo who was top 10 at the time, Nalbandian could've gone 5 out of 5 against top 10 players in that tournament.
Nalbandian also beat 4 top 10 players in Paris just weeks later and 5 top 15 players.