Former Wimbledon champion Simona Halep booked her place in the semi-finals of the WTA Birmingham grass-court event with a straight sets win over Britain's Katie Boulter on Friday.

Boulter had been in career-best form at the tournament, defeating Alison Riske in the first round of the Wimbledon warm-up before knocking out former top-10 player Caroline Garcia.

But second seed Halep ultimately proved too strong in a 6-4, 6-1 victory.

The 30-year-old Romanian, however, did not have things all her own way in a tightly-contested first set.

Boulter, who only returned from nearly three months out with a leg injury at Nottingham last week, kept pace with Halep for the opening eight games.

The 25-year-old, to her credit, saved three break points at 4-4 only to double fault on the fourth.

That proved to be the cue for Halep to pull away in what is her first grass-court event since a superb straight sets win over Serena Williams in the 2019 Wimbledon final.

"She's clearly one of the best tennis players out there," said Boulter of Halep.

"So, for me to be able to stand out there and feel like I can compete and win the match -- I really did feel if I brought a bit more game today, then it would have been closer and it would have been a tough match for both of us."

Halep will now play Brazil's Hadda Maia -- winner of last week's Nottingham Open -- in the semi-finals.

The world number 32 extended her winning streak on grass to eight matches with a 6-3 6-2 victory over Italian third seed Camila Giorgi.

Sorana Cirstea made it a day of double celebration for Romania by also reaching the semi-finals after coming from a set down to defeat Donna Vekic 5-7, 6-3, 6-4.

Cirstea will face Zhang Shuai in the last four following the Chinese eighth seed's 7-5, 6-4 win over Ukraine's Dayana Yastremska.

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© Agence France-Presse