Spanish tennis star Rafael Nadal has asserted his authority on court and defeated Switzerland's Stan Wawrinka 7-5, 7-6(4) in the Round of 16 at the Masters 1000 in Toronto.Nadal, however, had to dig deep to control the game as after winning the first set, Wawrinka was ahead in the second by breaking Nadal's serve but the Spaniard did the same and equalized the score to six games all on Thursday, reports Efe.In the tie-breaker, Nadal came forward and had three match balls, the second of which won the match after two hours and eight minutes.In other matches of the day, Greece's Stefano Tsitsipas knocked out Wimbledon champion Novak Djokovic from Serbia.Djokovic, who has won in Toronto four times, after losing the first set it appeared he could redeem himself in the second and break the tie after equalizing the score.However, in the third and final set Tsitsipas dominated the court from beginning to end claiming victory with 6-3, 6-7 (5-7) and 6-3 ending Djokovic's winning streak.Other winners were Bulgaria's Grigor Dimitrov who defeated the American Frances Tiafoe 7-6 (1), 3-6 and 7-6 (4) and Croatia's Marin Cilic who defeated Argentina's Diego Schwartzman 6-3 and 6-2, making him Nadal's next rival.