Nov 15 (Reuters) - World number one Novak Djokovic began his quest for a sixth title at the season-ending ATP Finals with a 7-6(4) 6-2 victory over Norway"s Casper Ruud in their round robin encounter in Turin on Monday. Djokovic suffered a fall and lost his opening service game but recovered to find his rhythm against Ruud, who is making his debut at the event following five tournament wins this season. "It was strange. I played a good forehand and came into the net and had a comfortable overhead. I slipped, tripped, dropped my racquet and lost my serve," Djokovic said. "The conditions here are tough. If you lose your serve, it"s difficult to get it back. But I managed to stay in. I"m pleased with the way I handled the match." Ruud"s powerful forehand helped him keep pace with Djokovic for much of the first set, but he was outplayed in the tiebreak as the 20-times major winner forced his 22-year-old opponent into a string of errors to take the opener. It was plain sailing in the second set for Djokovic, who broke in the first game and dominated the longer rallies as Ruud struggled on serve before eventually going down in an 91 minutes. Djokovic was later presented with the year-end world number one trophy for a record seventh time, bettering the mark set by 14-times Grand Slam champion Pete Sampras. "I was four or five when I saw Sampras play at Wimbledon for the first time. I asked for a racquet and fell in love with tennis. To know that I hold this record now, after Pete, it"s incredible," said the 34-year-old. In the day"s second singles match, Greek world number four Stefanos Tsitsipas suffered a disappointing start as he was beaten 6-4 6-4 by Russia"s Andrey Rublev.