Djokovic hit 15 aces and 31 winners in a commanding win over 33-year-old Zeballos, who was a top 40 player in 2013 but was playing at Wimbledon ranked a lowly 126.
When rain forced the tie to be postponed on Wednesday, Cilic was leading by two sets against an opponent who had never won a match at Wimbledon before this year.
There were a few scary moments in the early going, with Williams at one point down 5-3 in the first set and Mladenovic getting the better of her. "She played really well".
Cilic was runner-up to Roger Federer previous year and showed great form by beating Novak Djokovic in the Queen's Club final last month.
"Serena is my idol", Rodina said.
Keys, who was the US Open runner-up past year, crashed out 7-5 5-7 6-4 to the Russian on a baking hot Court Three.
Nadal won only 64 per cent of points on his first serve and faced 13 break points - including three in the first game of the match - but he saved 11 of them and converted five of his own to wrap up the win in under 2 1/2 hours on Centre Court. She then broke back to level the third set at 4-4, but Rodina immediately earned another break and served out the victory.
In the first point of the breaker, Buzarnescu ended a rally by plopping a forehand into the net, and after Pliskova followed up by holding her two service points for 3-0, the set was slipping away from the Romanian. I thought I did very well today.
He is on a great run at Wimbledon since the start of 2017, winning 29 consecutive sets here which is his second longest streak after 2005-2006 when he rattled off 34.
Makarova, who made the quarter-finals four years ago, beat a weary-looking Lucie Safarova of the Czech Republic 4-6, 6-1, 6-4.
Zverev beat Taylor Fritz of the USA 6-4, 5-7, 6-7 (0), 6-1, 6-2 in a match that was suspended on Thursday after the third set.
The Israeli tennis star Dudi Sela was beaten Tuesday by world number one Rafael Nadal in the first round of the Wimbledon Grand Slam tournament, in his third loss to the Spaniard in three career matches.