The American started poorly against the fourth-seeded South African, who blasted seven aces in a dominant opening set in which he raced through his service games and broke the 26th-ranked Sock in the fourth and sixth games.

Sock settled in the second set and improved his return as Anderson lost range and accuracy, tying up the quarter-final on his second break and set point opportunity in the 10th game.

Anderson served better in the decider but Sock eked out another break, again in the 10th game, to seal the contest in 98 minutes.

Twice champion John Isner of the United States will not be in the last four after losing the third quarter-final 7-5 2-6 6-3 to Roberto Bautista Agut, despite firing down 17 aces.

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