Dan Evans will meet fellow Brit Cameron Norrie at the San Diego Open on Thursday after beating Kevin Anderson 7-6 (11), 7-5 in two hours and 18 minutes.
Anderson, who reached the Wimbledon final in 2018 and US Open in 2017, slammed down 13 aces in the first set before a marathon tie-break which Evans clawed back on three occasions to win it on his fourth set point.
The second set was also tight with the decisive break for Evans arriving in the 12th game when he converted his third break point to win the match.
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"It was a tough tie-break, I think I was a little fortunate to come through that one and the first set," Evans said afterwards.
"But I played a good, solid second set and hung in pretty well. I was pretty happy with that."
Evans and Norrie have met just once on the ATP tour and that came at the Australian Open back in January which the latter won in four sets.
Andrey Rublev is also through to the quarter-finals with a 6-2, 6-1 win in 62 minutes against American wild card Brandon Nakashima.
Harriet Dart has been knocked out of the Chicago Fall Tennis Classic second round after a 6-3 6-4 defeat to Veronika Kudermetova.
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