STOCKHOLM — On the day Wimbledon introduced final-set tiebreakers, the player behind the two longest ever matches at the All England Club needed yet another one to advance to the semifinals of the Stockholm Open.

Big-serving John Isner won his second all-American matchup of the week in the Swedish capital, beating Tennys Sandgren 7-6 (8), 6-7 (5), 7-6 (2) in the last of the quarterfinals on Friday. All six sets played by the top-seeded Isner at the tournament have gone to tie-breakers.

Two epic matches involving the big-serving Isner at Wimbledon likely prompted the Grand Slam to announce earlier Friday that final-set tiebreakers will be played at the grass-court event from next year, when the score reaches 12-12 in the decider. He beat Nicolas Mahut 70-68 in the final set of a match that took more than 11 hours in 2010, and lost 26-24 to Kevin Anderson in the fifth set in the semifinals this year.

They are the two longest matches in the history of a tournament that began in 1877.

Both of Isner's wins in Stockholm have been hard-fought and involved late-night finishes.

"It was very tough," said the 10th-ranked Isner, who beat Bradley Klahn 7-6 (2), 6-7 (5), 7-6 (5) in the second round on Thursday. "It's similar to last night — very late.

"I need to take care of myself and go to bed."

Isner concluded the march of the top three seeds into the semifinals.

Stefanos Tsitsipas, the third seed from Greece, beat Philipp Kohlschreiber of Germany 6-3, 7-6 (4) and second-seeded Italian Fabio Fognini advanced after his opponent, Chung Hyeon, retired during their match. Fognini was leading this year's Australian Open semifinalist 7-5, 2-1.

In the other quarterfinal, fourth-seeded American Jack Sock lost 4-6, 6-3, 6-4 to Latvian Ernests Gulbis, the 2014 French Open semifinalist, who next takes on Isner.