Bernard Tomic claimed his biggest scalp in five years as he beat world No.7 Kei Nishikori to set up a Cincinnati Masters quarter-final against two-time Olympic champion Andy Murray.
Tomic, who skipped the Olympics and lost first up in Mexico last week, outlasted Rio Games bronze medallist Nishikori 7-6 (7-1) 7-6 (7-5) on Thursday in a welcome show of form 11 days out from the US Open.
Nishikori was 23-year-old Tomic's highest-ranked victim since Wimbledon in 2011, when he upset then world No.5 Robin Soderling.
However it's the second time the Queenslander has beaten Nishikori this year. He also ousted him from the season-opening Brisbane International when the Japanese star was ranked No.8.
Top seed Murray later had little trouble dispatching Kevin Anderson 6-3 6-2, as he extended his winning streak to 20 with his 600th career victory on the ATP Tour.
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World No.21 Tomic's serve was again on song as he approaches the final major of the year as he sent down 10 aces and was broken just once, early in the first set.
Fifth seed Nishikori wasn't the only big gun who struggled, with an injured Rafael Nadal knocked out by teenager Borna Coric 6-1 6-3 and second seed Stan Wawrinka losing to Grigor Dimitrov 6-4 6-4.
Nadal was visited from the trainer after his opening set, and his performance made for a sharp contrast to the Spaniard's gold-medal doubles success last weekend at the Rio Games.
The winner of 14 grand slam titles said he was "at the limit" after Rio and it was clear he was not ready.
"It was not easy to take the decision to not come here after the Olympics," he said. "I didn't want to be back home."
He now has little time to recover and prepare for the US Open, having missed two months of play since quitting the French Open with a left wrist injury.
Steve Johnson took the top American ranking from John Isner through a knockout of seventh seed Jo-Wilfried Tsonga 6-3 7-6 (8-6).
Austrian eighth seed Dominic Thiem advanced on a walkover when Gael Monfils withdrew with back pain.
