Eighth-seeded Jack Sock has booked his place in the semi-finals of the ATP event in Washington after a straight-sets win over Milos Raonic.
The big-serving American, beaten in the quarter-finals in the previous two years, saw off third-seeded Canadian 7-5 6-4 in an hour and 25 minutes.
Sock will face Kevin Anderson for a place in the Washington final after the South African veteran ended Yuki Bhambri's interest in the competition.
Anderson, the 15th seed, defeated Indian qualifier Bhambri 6-4 4-6 6-3.
"It was a really tough match tonight. Conditions were hot, it was a little gusty, balls were flying," Anderson said.
Second-seeded Kei Nishikori shrugged off fatigue and saved three match points before beating unheralded American Tommy Paul 3-6 7-6 (10-8) 6-4.
Nishikori seemed destined for an early exit in the fierce Washington heat when 20-year-old Paul brought up match point at 5-3 in the second set with a backhand winner down the line.
However, the Japanese star survived with an audacious drop shot before staving off two more match points in the tiebreak and taking the second set.
That appeared to break the spirit of the 225th-ranked Paul and Nishikori, who had post-midnight finishes to his previous two matches at the tournament, took control in the final set to advance to Saturday's semi-finals.
Next up for the 27-year-old is another 20-year-old in Alexander Zverev.
The German fifth-seed had too much in his arsenal for Russian Daniil Medvedev and won their quarter-final 6-2 6-4 in less than an hour.
"I felt good from the start to the end. It was a great match for me," world number eight Zverev told Tennis Channel.
"I knew I had to take his time away, play my aggressive game and dominate as much as I could and it worked out very well today."
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