Radwanska cruised through the first set but faced heavy resistance in the one-hour second set as the No.13-seeded Ivanovic stayed with her, even serving for the set at 6-5; but the No.4-seeded Radwanska broke at 15 and closed the 61 76(6) win out in the breaker to make the quarterfinals.
"Ana really started to play much better in the second set - she wasn't making any easy mistakes in the second set," Radwanska said after the match. "I really needed to just play my game. She wasn't giving me any free points and it was really close. So I'm very, very happy I could close this and win in two sets, because you never know what's going to happen if you end up going to a third set."
The win over Ivanovic was Radwanska's 15th win of the year - she was one of the match win leaders early on last year as well. "I had a really great season last year, and obviously the start of this year as well," she said. "I'm very happy I've played so well from the beginning of the year, having two titles in a row in the first two tournaments - it never happened before, so I'm really happy about it all.
"I've had a lot of matches this year, so it's been busy, but I think it's a good problem."
"It wasn't great tennis out there today - the wind was a huge factor," Wozniacki said afterwards. "It seemed the wind took more on my court than it does on center, because you have the fence behind and when the ball is higher than the fence when you throw the ball up to serve, it goes anywhere. I mean, it was very windy out there. To be honest it was just about getting the ball in play today.
"I was just trying to get it in and hoping for the best. It was a struggle, but I got through it."
Azarenka's win over McHale was the sixth time in her career she has won a match by a 60 60 scoreline - she scored two in 2008, one in 2009 and two more in 2011. "I felt like I came out very focused, with a good mindset and a good game plan," Azarenka said. "There were a few close games, but I felt like I was really taking advantage of every opportunity I had and not letting her play her game.
"That was the key for me today, to not let her play her game, because she's a very good mover, a very good grinder - she also has a big weapon that can come from anywhere with her forehand."
Errani seemed headed for a simpler straight set win over Hantuchova as she built a 75 42 lead with points for 75 52; but Hantuchova, a former Top 5 player, won seven of the next nine games to take the second set and go up 2-1 in the third. Errani reeled off five games in a row to finish the job.