Favorite Carlos Alcaraz of Spain booked his place in the Next Gen semifinals with a 4-3 (4) 4-1 4-3 (4) win over Brandon Nakashima of the United States on Wednesday.
Alcaraz is living up to his billing as top seed and has not dropped a set in his two Group A matches at the round-robin tournament for the top 21-and-under players on the ATP Tour.
He was taken to two tiebreaks by Nakashima but his powerful serve helped him to prevail in less than 90 minutes, with 10 aces. Alcaraz won the match when Nakashima could only return another potent serve into the net.
The 18-year-old Alcaraz has moved more than 100 places up the rankings this season to No. 32 and reached the U.S. Open quarterfinals.
Nakashima, who beat Francisco Cerúndolo in their opener, will face Holger Rune of Denmark on Thursday for the other semifinal place from Group A.
Rune earlier kept his hopes alive by beating Cerúndolo of Argentina 4-1 4-2 1-4 4-1.
Rune stormed into a 3-0 lead in the opening set and -- apart from a brief lapse of concentration in the third -- never looked back as he imposed his aggressive baseline game, serving out the match to love to win in just 78 minutes.
The Group B matches in the eight-man tournament were taking place later, with another American in Sebastian Korda playing Sebastian Baez of Argentina. Both won their openers on Tuesday.
Home favorite Lorenzo Musetti was playing Frenchman Hugo Gaston.
It is the fourth edition of the tournament in Milan. It was cancelled last year because of the coronavirus pandemic. The ATP Finals will also be in Italy, in Turin next week.
There are different rules at the Next Gen Finals, including on-court coaching, no-Ad scoring, medical timeout limits, and Hawk-Eye making all the line calls.
The most drastic change is the shorter set, where the first to four games takes the set, with a tiebreak at 3-3.
This year there are also shorter warm-ups, ensuring matches begin just one minute after the players enter the court, while bathroom breaks are timed to three minutes.