MIAMI, March 27 — Defending champion John Isner reached the Miami Open quarter-finals with a 7-6(5) 7-6(3) win over Britain's Kyle Edmund yesterday while Nick Kyrgios was given a point penalty for an audible obscenity during his loss to Borna Coric.

The obscenity by Australian Kyrgios, who produced perhaps the shot of the tournament early in his 4-6 6-3 6-2 loss to 11th-seeded Coric, was apparently directed at a spectator and the penalty put him down a double break in the third.

It was the latest incident in Miami for Kyrgios, who had already made headlines for controversial underhanded serves, a verbal spat with a spectator who was heckling him and firing off an expletive-laden rant at an umpire during a doubles match.

Kyrgios trailed 3-1 in the opening set to Coric but looked energised when, after sending a no-look volley over the net, he charged toward the back corner of the court where he executed an audacious 'tweener' that caught a flat-footed Coric off guard.

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While the 27th-seeded Australian picked up his game it proved only temporary as Coric coolly regained control before securing victory to draw level in four career head-to-head meetings with Kyrgios.

Up next for Coric will be a clash with Canadian Felix Auger-Aliassime, who beat Georgian 17th seed Nikoloz Basilashvili 7-6(4) 6-4 to become the first qualifier to reach the last eight in Miami since Guillermo Canas in 2007.

Big-serving Isner fired down 17 aces and won 81 per cent of his first-serve points to reach the quarter-finals without dropping a set through three matches in Miami.

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For a moment, however, it appeared the American had lost momentum after he failed to serve out the opening set while leading 5-2 and then was forced to recover from a double mini-break down in the first tiebreak.

Isner will next face the winner of a clash between six-times champion Novak Djokovic and Spanish 22nd seed Roberto Bautista Agut.

Swiss fourth seed Roger Federer will cap the night session when he faces Russia's Daniil Medvedev. — Reuters