A day before the Citi Open started, 2011 US Open champion Samantha Stosur spent an hour hitting on court with world No.173 Jessica Pegula.

On Friday (Saturday AEST), in the Washington hardcourt tournament’s quarter-finals, wildcard Pegula upset the top-seeded world No.14 Stosur 7-6 (4) 6-3 to get to a WTA semi-final for the first time.

Pegula said that spending time with Stosur before the tournament was a boost, because it gave a little insight to the sort of professionalism needed to reach the upper echelon of the tour.

“She probably doesn’t want to hear that, but it really helped me practising with her,” the 22-year-old Pegula said.

Stosur led 4-1 in the opening tiebreaker before losing six consecutive points to drop that set.

The only break of the match came in the next-to-last-game, when Pegula went up 5-3, then served out the match.

Pegula, whose parents own the NFL’s Buffalo Bills and NHL’s Buffalo Sabres, had lost seven of her past eight matches before arriving in Washington.

On Saturday (Sunday AEDT), she will face Lauren Davis for a berth in the final.

Davis beat Camila Giorgi 6-4 6-4 in Friday night’s last quarter-final.

The other semifinal at the hard-court tournament will be No.6-seeded Yulia Putintseva against No.7 Yanina Wickmayer.

Wickmayer beat No.4 Kristina Mladenovic 4-6 6-3 6-4, while Putintseva beat Risa Ozaki 6-4 6-2.