Novak Djokovic thought he was "pretty flawless" in his first match of the Serbia Open, but Rafael Nadal was given a scare in his clash with qualifier Ilya Ivashka at the Barcelona Open.
World number one Djokovic suffered a shock third-round exit to Dan Evans at the Monte Carlo Masters last week but ruthlessly dispatched Kwon Soon-woo 6-1 6-3 in his home city of Belgrade.
Djokovic broke his opponent five times to set up a meeting with eighth seed and fellow Serbian Miomir Kecmanovic, who battled past qualifier Arthur Rinderknech in three sets, in the quarter-finals.
"I thought it was a pretty flawless performance," Djokovic said. "I moved well, I was mixing up the pace quite well, making him play. I served well in the important moments, [and] overall I just felt great."
On playing in front of his family and friends, the two-time Serbia Open champion added: "It gives you an extra push, an extra motivation, energy to really give your best and leave it all out on the court.
"I think also that made me feel comfortable and confident on the court and I played really good. I'm really pleased with the quality of tennis."
Second seed Matteo Berrettini defeated fellow Italian Marco Cecchinato 6-4 6-3 and will face either Filip Krajinovic or Nikola Milojevic in the last eight of the clay-court tournament.
Over in Barcelona, Nadal – an 11-time champion at the event – was out to make a statement after a rare defeat on the dirt to Andrey Rublev in Monte Carlo.
But the 'King of Clay' needed two hours and 20 minutes to fight back against the unheralded Ivashka 3-6 6-2 6-4 to reach the round of 16, where he will face Kei Nishikori. Nadal is now 62-4 at a tournament where he once won 41 straight matches.
Second seed and Monte Carlo champion Stefanos Tsitsipas hammered Jaume Munar 6-0 6-2, while third seed Rublev - runner-up to the Greek on Sunday - joined Pablo Carreno Busta (6) and Alex De Minaur (14) in making it through.
Evans was unable to follow up his run in Monte Carlo with the 16th seed beaten by Corentin Moutet in a lengthy three-setter, while Fabio Fognini (9) was defaulted for unsportsmanlike conduct after verbally abusing a line official when trailing 6-4 4-4 to Spanish qualifier Bernabe Zapata Miralles.