He is serving well, winning 84% of first-serve points here, and just over half on his second serve, which has been a weakness.
People used to flock to Isner's college matches to behold his serve, which has been clocked at 140 miles an hour.
But at 15-15 Wawrinka's serve, which has been hugely improved this set, gifts him two quick points, and another ace gives him the set!
He closed out a 6-7 (5), 6-0, 6-0, 6-4 victory with Higueras in the stands, without dropping his serve, which has been one of his strengths so far.
His serve, which has been clocked as fast as 156 miles an hour, rocketed through the thin air of the Colombian capital, which has an elevation of 8,612 feet.
What also let him down here was his serve, which had been improving.
Phau's serve, which had been lacking in the early rounds, was dominant in the first set.
Schwartz's serve, which had been stellar throughout the tournament, deserted her midway through the first set, and she looked to be in trouble early in the second set when her serve was broken in the first game.
His serve, which had been impeccable, also deserted him and he served two double faults to give Federer a way into the match.
But he could not maintain his consistency and his serve, which had been such a weapon in the early stages, faltered to allow Ferrer to turn the screw.
