Roger Federer defeated a hobbling John Isner 6-1 6-4 for his 101st career title at the Miami Open on Sunday.
Holder Isner struggled to continue late in the second set, hampered by pain in his left foot.
He said afterwards that he was concerned that he may have broken bones.
Federer, who won his fourth Miami title, broke Isner three times in a blazing opening set.
But the American fought back in the second, levelling the set 3-3 and 4-4 before the pain made it difficult to continue.
Federer took the final two games for the victory.
"It was a dream start, relaxing my nerves," the Swiss said in a courtside interview.