The No.12-seeded Ivanovic faced Svetlana Kuznetsova on Stadium court and passed with flying colors, keeping her winners and unforced errors completely even - 24 to 24 - in prevailing, 63 63.
"I really had to stay focused on every point and stay in the moment, and I'm very happy I was able to win tonight," Ivanovic said. "I always love coming here and competing here. It's always fun. And this year I really felt I was playing good tennis coming in, so I'm really enjoying my time here this year."
Ivanovic, a former World No.1, and Kuznetsova, a former World No.2, were playing for the 11th time - and Ivanovic seems to have Kuznetsova's number, now improving to 8-3 in their head-to-head series.
Meanwhile on Court 3, the No.8-seeded Errani was in crushing form, dropping just one game - and even holding a game point in that game - en route to a 48-minute, 61 60 victory against Simona Halep.
"I think I played a really good match - I was very focused from the beginning and it went very well for me," Errani said after the match. "I did very well in pretty much everything today - from the baseline I was running very fast, and I had to be running fast because she was always trying to push me from the backhand, but I was at every ball and was able to take it from my forehand a lot on that side."
Errani is the WTA's match win leader this year, her win over Halep being her 23rd match win of the year. Agnieszka Radwanska is second on the list and two wins behind the Italian with 21 wins.
Ivanovic leads Errani in their head-to-head, 2-1, though Errani did win their most recent meeting.
"I think she's a better player now than the last few times we played," Ivanovic said. "The last time we played was at the French Open last year and she beat me, then she had a great run to the final. It's going to be very, very tough against her. I have to be patient and focused and move very well."
Speaking of Italians, Errani's countrywoman Roberta Vinci was also among the winners on Sunday, though she had to fight a lot harder to do it. The No.15-seeded Vinci needed almost two and a half hours and came back from 2-0 down in the third to edge No.20 seed Carla Suárez Navarro, 57 64 64.
"It was a tough match," Vinci said. "It was tough conditions out there, especially with a lot of wind at the beginning, and she has an unbelievable backhand too. I had a lot of chances in the first set but lost it, but from the second set I stayed very focused and just played my game, staying aggressive.
"This is my first victory against her, so I'm very happy."
Next for Vinci is No.32 seed Alizé Cornet, who won through earlier in the day against Lauren Davis, 26 63 62. Cornet broke away from 26 33 with seven straight games to take the second set and build a 4-0 lead in the third, then never really looked back to finish off the tenacious American lucky loser.
Vinci has beaten Cornet in both of their previous meetings, and by identical 62 63 scorelines.