Top seed Alexander Zverev took “a huge step up” to dismantle Alex de Minaur 6-4, 6-4 on Thursday and roll into the Shanghai Masters semi-finals.

He will play Alejandro Davidovich Fokina, who advanced when France’s Arthur Gea retired injured from their quarter-final after 22 minutes.

Zverev, who will end the year at world number one, was tested by the Australian’s speed in the first set but sent down a string of dazzling forehands to convert a break point in the fifth game.

Despite a double fault, the German saved three break points in a row to hold serve and was rewarded in the 10th game, taking the first set with a buttery backhand at the net.

Zverev refused to relent in the second set, setting up another break point in the seventh game to go up 4-3 when De Minaur served into the net.

The 27-year-old Australian clung on for a bit longer, but Zverev wasn’t sticking around, clinching victory on the first match point.

“Good match for me,” Zverev, 29, said. “Very satisfied with my level… it was a huge step up from the last couple of matches.”

Zverev needed three sets to win his two previous matches.

In the other last-eight fixture, France’s Gea was in the biggest match of his career when he quit his match with muscle issues.

The 21-year-old took a medical timeout for work on his lower right side when he was down 1-4 in the first set.

He returned to play but ended the match minutes later.

“I felt this morning, during a warm-up, pain in the psoas,” he said, referring to a muscle in the lower back.

He said he received “treatments” and decided to step on court despite being unsure about his fitness.

“I tried from the beginning, but it was not enough to play full and too dangerous for the end of the season.

“I’m really sad, but it’s the best choice I could make,” said 56th-ranked Gea, who was playing in his first tournament at the prestigious ATP 1000 level.