US Open 2014: John Isner shows exactly why he is men’s ace among big servers

American hits 30 in straight sets victory over Jan-Lennard Struff

The world No 15 John Isner has a good strike rate with his second as well as first serves (Getty Images)

Andy Murray is among those who regard John Isner’s serve as the best in the business and the 29-year-old American underlined the point at the US Open by hitting 30 aces during a convincing straight-sets victory over Germany’s Jan-Lennard Struff.

Isner, who won 7-6, 6-4, 6-2, served at speeds of up to 138mph, won 87 per cent of points when his first serve found the target and had to defend only one break point in the whole match. Struff, the world No 77, played well enough when he was able to get into the rallies, but that was all too rare on Isner’s serve. The tie-break, which Isner won 7-5, was typical as the 24-year-old German barely got a racket on his opponent’s serves.

Although Isner is only fifth on the Association of Tennis Professionals’ list of first-serve points won in 2014 – Ivo Karlovic, Milos Raonic, Sam Querrey and Marin Cilic are all ahead of him – Murray believes the world No 15’s serve is the best.

“He serves huge first serves but the difference between him and the other guys is the second serve,” Murray said. “He serves quite a lot of second-serve aces. He gets good work on the second serve. Maybe Karlovic gets a few more aces with his first serve because he serves and volleys more and has the momentum going forward a little bit, but second serve and overall I would say that John’s is the best.”

Isner, who hit 26 aces in a straight-sets victory over Marcos Giron in the first round, now meets Germany’s Philipp Kohlschreiber, who benefited from Michael Llodra’s retirement with an elbow injury after the Frenchman, playing in his last Grand Slam tournament, had lost the first set.

Querrey is also through to the third round after beating Spain’s Guillermo Garcia-Lopez 6-3, 6-4, 6-4, but the American faces a huge challenge next time out against Novak Djokovic. The world No 1 cruised to a 6-1, 6-3, 6-0 victory over France’s Paul-Henri Mathieu.