American world number four Jessica Pegula has made it through to the semi-finals of the WTA event in Berlin, beating fellow American Madison Keys in straight sets on Friday.
Pegula, who won the title in Berlin last year, came through 7-6(5), 7-6(8) in hot conditions in the German capital.
The two had not met since Pegula knocked Keys out of the Australian Open in January. Both players broke serve once in the opening set before it went to a tiebreak, which Pegula took.
Pegula moved into a 4-2 lead in the second set, but Keys fought back to force another tiebreak. Pegula won it 10-8, stretching her winning run against fellow Americans this year to seven matches in a row.
The 32-year-old will face either world number one Aryna Sabalenka or Nikola Bartunkova in the semi-finals on Saturday.
Also on Friday, world number eight Elina Svitolina plays Alexandra Eala, who knocked out Elena Rybakina on Thursday. The last quarter-final sees eighth seed Linda Noskova take on Spanish wildcard Paula Badosa.
