Top seed Novak Djokovic made quick work of Tennys Sandgren at the Western and Southern Open on Tuesday, never dropping a serve to a 6-2 6-4 win over the American, while big-serving Milos Raonic enjoyed a straight sets win over Andy Murray. 

Djokovic broke Sandgren three times to reach the quarter-finals and extended his win-loss record to 20-0 this year. 

"All in all it was just a great performance," said the Serb. "I felt better and I played better than I did last night. Everything is going in the right direction."

Next up for Djokovic is German Jan-Lennard Struff, who outlasted David Goffin 6-4 3-6 6-4 earlier on Tuesday. 

Murray had an impressive win over fifth seed Alexander Zverev on Monday but never found his rhythm against Raonic. 

The Canadian dominated on serve, firing 10 aces and winning almost 90% of his first-serve points, to advance to the quarter-finals 6-2 6-2 in a rain-interrupted match that marked his first win over the Briton since 2014 at Indian Wells. 

Defending champion Daniil Medvedev looked sharp in his stress-free 6-3 6-3 dismantling of qualifier Aljaz Bedene to reach the quarter-finals. 

Stefanos Tsitsipas defeated John Isner 7-6(2) 7-6(4) and Reilly Opelka beat sixth seed Matteo Berrettini 6-3 7-6(4). Roberto Bautista Agut and Filip Krajinovic also advanced. 

On the women's court, Serena Williams was sent spinning out of the Western and Southern Open by Maria Sakkari on Tuesday after the Greek rallied from a set down to beat the 23-times Grand Slam champion 5-7 7-6(5) 6-1 and reach the quarter-finals.  

Sakkari next faces Briton Johanna Konta, who got past Vera Zvonareva 6-4 6-2.  

Earlier, Naomi Osaka put on a solid serving performance to beat 20-year-old Ukrainian Dayana Yastremska 6-3 6-1 and advance to the quarter-finals, where she will face Anett Kontaveit. 

Meanwhile, China's Xu Yifan partnered with American Nicole Melichar to defeat Cori Gauff and Catherine McNally to reach the third round of the women's doubles event. 

Xu and Melichar, seeded second in the event, will next face Russian duo Anna Blinkova and Veronika Kudermetova in the quarterfinals. 

The ATP Masters 1000 tournament is being played at Flushing Meadows in New York this year instead of Cincinnati due to the COVID-19 pandemic. 

No spectators were present at the event, which is the final tune-up before the U.S. Open Grand Slam, which begins on August 31. 

(With input from agencies)