LONDON — All it took was a couple of questionable calls for Novak Djokovic to snap at the chair umpire in the second game of his third-round match at Wimbledon.

“That’s two points in a row at the beginning of the match,” Djokovic said before telling official Jake Garner: “Focus, please!”

That would have been good advice for Djokovic himself. Maybe he was a bit on edge because this was the stage at which, as a two-time defending champion, he lost at the All England Club a year ago. On Saturday, Djokovic briefly fell behind by an early break before zipping past Ernests Gulbis of Latvia 6-4, 6-1, 7-6 (2) to earn his 10th berth in the tournament’s second week.

Right after his, er, conversation with Garner, Djokovic lost a service game to trail 2-1. He later fell behind 4-2 in the opening set. But from there Djokovic used a nine-game run to seize control and wasn’t broken again.

“As soon as you give a guy like Novak the tools to step on the gas, he will step on the gas,” said Gulbis, who has been a top-10 player and a French Open semifinalist but missed chunks of time because of injuries, dropping his ranking outside the top 500. “And he just goes, and he doesn’t look back.”

Three of Djokovic’s 12 major championships have come at Wimbledon, and after a real dip in results over the past 12 months, he hasn’t dropped a set in the event this year.

After the grass-court Grand Slam tournament’s traditional middle Sunday off, he will face 51st-ranked Adrian Mannarino for a place in the quarterfinals.

All 16 fourth-round singles matches are scheduled for Monday – Wimbledon is the only major that does it that way – including these in the bottom half of the men’s draw: No. 3 Roger Federer vs. No. 13 Grigor Dimitrov; 2016 runner-up Milos Raonic vs. No. 10 Alexander Zverev; and 2010 runner-up Tomas Berdych vs. No. 8 Dominic Thiem.

Federer, like Djokovic, has won every set he’s played this week, including Saturday’s 7-6 (3), 6-4, 6-4 win against No. 27 Mischa Zverev, Alexander’s older, left-handed, serve-and-volleying brother.

The matchups on the top half of the men’s draw are Andy Murray vs. Benoit Paire, Rafael Nadal vs. No. 16 Gilles Muller, No. 7 Marin Cilic vs. No. 18 Roberto Bautista Agut, and No. 24 Sam Querrey vs. Kevin Anderson.

Women’s fourth-rounders: five-time champion Venus Williams vs. No. 27 Ana Konjuh, No. 1 Angelique Kerber vs. No. 14 Garbine Muguruza, No. 2 Simona Halep vs. two-time Australian Open champion Victoria Azarenka, French Open champion Jelena Ostapenko vs. No. 4 Elina Svitolina, No. 6 Johanna Konta vs. No. 21 Caroline Garcia, No. 7 Svetlana Kuznetsova vs. 2012 runner-up Agnieszka Radwanska, No. 5 Caroline Wozniacki vs. No. 24 CoCo Vandeweghe, and Magdalena Rybarikova vs. Petra Martic.