Turin, Nov 15 : Italian Matteo Berrettini's campaign in the year-end Nitto ATP Finals began on an inauspicious note as the home star was forced to retire early in the second set of his match against Germany's Alexander Zverev due to an injury to his left oblique, in the Red Group of the elite eight-player tournament. Tokyo Olympic Games gold medallist Zverev won a tightly-contested first set 7-6(7) in 79 minutes and led 1-0 in the second set when Berrettini was unable to continue late on Sunday night (IST). Following a medical timeout, the Italian attempted to continue, but after only one more point, he walked to the net to shake hands. Zverev climbed over the net to console him. "I don't really know what to say, because this is the worst feeling a player can have," Zverev said in his on-court interview. "You play all year long to qualify for this beautiful tournament. For Matteo playing at home, this is the worst feeling I think he will ever have in his career," the German told nittoatpfinal.com. "I thought the first set was incredibly high-level tennis. This is all not important," Zverev said. "The most important thing is that both players at the end of the match can shake hands and are healthy. Today this is not the case. I think a lot of you guys, everybody here in Italy looked forward to seeing (Matteo) play all three matches, maybe the semifinals, maybe the final." Zverev moves to 1-0 in Red Group play and will next play defending champion from Russia Daniil Medvedev on Tuesday (November 16). The German, who triumphed at the season finale in 2018, is now 9-7 at the event. Both players blasted the ball from the baseline and looked calm under pressure. The Italian crowd was fully behind Matteo from the moment he walked onto the court. Zverev saved two set points when he served at 5-6, and on both occasions Berrettini missed a backhand return. The Italian's first set point was his best opportunity, but he lost balance as he leapt to return a second serve and launched the return well long. The German then rallied from 3/5 down in the tie-break and ultimately took the set after putting a forehand return from full stretch within inches of Berrettini's baseline. /IANS