Madrid, May 14: Switzerland's Roger Federer took back the No. 1 spot in the men's Association of Tennis Professionals (ATP) world singles rankings released on Monday after being second to Spain's Rafael Nadal for six weeks.Nadal dropped to second place after being defeated in the Madrid Open quarter-finals by Dominic Thiem of Austria 7-5, 6-3 on Friday, ending his bid for the tournament's sixth title and a record streak of 50 consecutive clay-court sets wins, reports Efe."I had to play an extraordinary match, and that's what I did. It takes a really good match to beat Rafa on clay, but I think a very important thing was that I went in with the attitude that I can beat him," Thiem said after Friday's match.Alexander Zverev maintained his third position, after the German claimed the title of the 2018 Madrid Open for the first time after winning 6-4, 6-4 over Thiem, who dropped to the eighth spot.The current top 10 ATP rankings and point scores are as follows:1. Roger Federer (Switzerland) 8,670 Points2. Rafael Nadal (Spain) 7,9503. Alexander Zverev (Germany) 6,0154. Grigor Dimitrov (Bulgaria) 4,8705. Marin Cilic (Croatia) 4,7706. Juan Martín del Potro (Argentina) 4,5407. Kevin Anderson (South Africa) 3,6608. Dominic Thiem (Austria) 3,5459. John Isner (US) 3,30510. David Goffin (Belgium) 2,930.