J.J. Wolf entered the Dallas Open at a career high of World No. 43, thanks in large part to his fourth-round run at the Australian Open. Now into his second-career ATP Tour semi-final, the American is up even higher at No. 37 in the Pepperstone ATP Live Rankings.

The 24-year-old upset second seed Frances Tiafoe 4-6, 6-3, 6-4 in Friday's quarter-finals, earning the best win of his career by measure of the Pepperstone ATP Rankings.

After dropping serve twice on nine break chances for Tiafoe in the opening set, the sixth-seeded Wolf did not face another break point until he served out the match. Down 15/40, he used an ace and a line-clipping inside-out forehand to force deuce, then finished the job with his 11th ace on his second match point.

"I usually don't think about the outcome, so I was just feeding off the energy of the fans and playing every point as hard as I could," Wolf said of his methodical comeback, donning a Southern Methodist University cap for his post-match interview in honour of the tournament's host site.

The American finished the match with 26 winners and 10 unforced errors, tightening up his game in the second and third sets.

While Wolf was out-aced by Tiafoe, 14 to 11, the former Ohio State star won 82 per cent of his first-serve points, seven percentage points higher than his opponent's mark. Wolf made 60 per cent of his first serves in the contest, at times trading power for placement.

"I've just tried to create a little more consistency," he said of his serve. "The fans might not like it when I'm not putting up 140 [mph] serves, but my coaches like it."

Wolf will meet another countryman in the semi-finals, with fifth seed John Isner awaiting after his 7-6(8), 7-5 win against Ecuador's Emilio Gomez.

Playing in his home city, Isner saved a set point at 6/7 in the first-set tie-break with a second-serve ace down the T, then clinched victory with the first break for either man in the match's final game. The American saved four break points, escaping a 15/40 hole once in each set.

In returning to the Dallas semi-finals for the second straight year, Isner also made some personal history: He won the 500th tie-break of his career, improving his tie-break record to 500-319. Those 500 wins are the most in the Open Era, with Roger Federer's 466 second on the list.

Gomez, the son of former World No. 4 Andres Gomez, was playing in his first tour-level quarter-final.

In evening action, top seed Taylor Fritz defeated seventh seed Marcos Giron 7-6(7), 3-6, 6-3 in an all-American quarter-final, avenging a loss at the same stage of the ATP 250 one year ago. Fritz did not create a break chance until he saw two in his first return game of the final set, converting on the second to take a 2-0 lead.

He quickly consolidated with a hold to love, and later used another love hold to serve out the match. With just one break point against him, Fritz dominated on serve behind nine aces and an 82 per cent win rate on first serve.

The battle for #InAttack shifted set by set as @Taylor_Fritz97 won a close one in Dallas, avenging his loss to Giron in the same event last year. #InAttack shows the percentage of shots played in attack #TennisInsights | @atptour pic.twitter.com/DqCiGSnUXc

— Tennis Insights (@tennis_insights) February 11, 2023

The Netflix Break Point star will meet China's Wu Yibing in Saturday's semis. Playing in his first tour-level quarter-final, Wu upset eighth seed Adrian Mannarino 6-3, 6-4, converting on all three of his break points in an efficient victory.

The 23-year-old has knocked off two seeded players in Dallas, beating third seed Denis Shapovalov in straight sets on Wednesday. He has moved up 14 places in the Pepperstone ATP Live Rankings this week to No. 83, up from his career high of World No. 97. Wu is set to become the Chinese No. 1 on Monday, when he will pass Zhang Zhizhen for the honour.