Roger Federer admits he faces a real battle to land the 101st title of his career with the in-form Daniil Medvedev next up after Serbian Filip Krajinovic was dispatched 7-5, 6-3 on Monday at the Miami Open.
The Swiss superstar produced an excellent all-round performance despite being tested by the world No 103, who belied his lowly ranking by producing some excellent tennis during an exciting first set.
Federer, however, stylishly weathered the storm to seal the win - the 52nd of his career in Miami - and set up an intriguing last eight match with the highly-rated Medvedev.
The Russian, who is at a career high ranking of 15, saw off American Reilly Opelka 7-6, 6-7, 7-6 and has won four ATP hard-court titles, including three since last August. Federer beat him twice last year but is already a fan.
"He's clever how he plays the court because he can play it up and down, and he's unusual when he plays from back," said the Swiss, who hit 14 aces and won an impressive 74 per cent of points on his first serve.
"It's a bit of a different approach.Thankfully I played him last year twice in Basel and Shanghai and I'm very impressed about his progress. I must say the last year has been unbelievable for him."
Elsewhere, No 24 seed Grigor Dimitrov was beaten by world No 77 Jordan Thompson in straight sets ensuring the Australian will meet 2018 Wimbledon finalist Kevin Anderson who beat Portugal's Joao Sousa 6-4, 7-6.
Halep downs Williams
Simona Halep, meanwhile, got the better of Venus Williams once again as the Romanian made light work of the 38-year-old American to book a place in the quarter-finals with a 6-3, 6-3 win.
"I was pretty strong with my serve and knew where to bother her," said the reigning French Open champion who will meet China's Wang Qiang in the last eight.
"When I saw I can win easy games with my serve, it gave me great confidence."
Bianca Andreescu, the 18-year-old Canadian sensation who won the title in Indian Wells, was forced to withdraw in the second set of her fourth round match with Anett Kontaveit.
Andreescu was 1-6 0-2 down before a shoulder injury ruined her chances of another run to the finals.
The Estonian will meet Taiwan's Hsieh Su-Wei who continued her excellent form with a 6-3, 6-7, 6-2 win over Caroline Wozniacki.
Petra Kvitova, the world No 3, booked her place in the last eight, beating Caroline Garcia 6-3, 6-3 in a match which was held up for one hour and 40 minutes because of rain in South Florida. Kvitova plays Australian Ashleigh Barty for a place in the semi-finals.
