Complex sentence: This was the first time a man made four consecutive grand slam finals since Rod Laver in 1969, if not for his loss to Pete Sampras in the 1999 Wimbledon final, Agassi would have won a non-calendar grand slam.
Split into simpler sentences: This was the first time a man made four consecutive grand slam finals since Rod Laver in 1969. If not for Agassi's loss to Pete Sampras in the 1999 Wimbledon final, he would have won a non-calendar grand slam.