American Taylor Fritz battled past Ben Shelton in three sets on Friday to reach the semifinals in Halle five days after losing the title match to his countryman in Stuttgart.
World No 9 Fritz won 6-7 (5/7), 7-6 (10/8), 7-6 (7/3) in two hours and 45 minutes in the traditional Wimbledon warm-up ATP event.
Shelton, the world No 5, beat the 29-year-old Fritz to claim his first career title on grass in the Stuttgart ATP tournament last Sunday.
It was a battle between the two American big servers, neither player was broken throughout the match, with each set win coming through tiebreaks.
Shelton triumphed in the opening set. Fritz, a career grass court specialist, fought back to claim the second, saving a match point to force a deciding set.
Shelton fell to the grass midway through the third set and limped back to his bench but was able to continue.
Fritz grew more confident as the match went on and was in control to win the third and final tiebreak.
Fritz will face either French Open champion and top seed Alexander Zverev or Raphael Collingon in the final four.
Later on Friday, world No 4 Felix Auger Aliassime plays Frances Tiafoe and fourth seed Daniil Medvedev faces Daniel Altmaier in the remaining quarterfinals.