Miami, March 27 : Australian Open finalists Danielle Collins broke Vera Zvonareva four times Saturday to reach the fourth round of the Miami Open WTA event. The highest-ranked American woman at No.11, and the No. 9 seed here at the Miami Open, Collins defeated qualifier Vera Zvonareva 6-1, 6-4 in 78 minutes. Collins had four aces and broke Zvonareva's serve three times on the Stadium court. Collins has been nursing various injuries this year, including back and abdominal ailments. Lately, she said, the after-effects of a viral illness have left her with significant neck pain. No.9 seed Collins will next play 8th-seeded Ons Jabeur in a clash between two of the three seeds left in the top half of the draw. Alison Riske also advanced on Saturday. Collins, who made the Miami semi-finals as a qualifier in 2018, was aggressive and exhibited superior groundstrokes, which kept Zvonareva under pressure. She won the first set before they needed a fresh set of balls. "There was obviously an emotional moment for me, the pain that I'm dealing with right now with this injury," she said in her on-court interview. "Just trying to work through that, I think is one of the hardest things we go through mentally when we're on the court. Because when we have that physical pain it distracts you from what you need to do, it holds you back in the big moments," she was quoted as saying by the WTA in a report. The 28-year-old American, one of only three seeds left in the top half of the draw, benefitted when the following top players all lost their first matches: No.1 Aryna Sabalenka, No.3 Anett Kontaveit, No.6 Karolina Pliskova, No.11 Elina Svitolina, No.11 Emma Raducanu, No.13 Angelique Kerber and No.18 Leylah Fernandez. No. 8 seed Jabeur, overcame Kaia Kanepi of Estonia 6-3, 6-0 in a third-round match while No. 22 seed Belinda Bencic of Switzerland defeated Heather Watson of Great Britain 6-4, 6-1 in a match that finished in just short of one and a half-hour. Meanwhile, four-time Grand Slam winner Naomi Osaka of Japan advanced to the next round without having to hit a ball when her expected Round 3 opponent, Karolina Muchova of the Czech Republic, was forced to withdraw from the tournament due to a left abdominal injury. As a result of the walkover, Osaka is into the fourth round in Miami for the second year running. Last year, she reached the quarterfinals in her best-ever tournament result. Muchova and Osaka were slated to play for the third time in their careers, having split the first two meetings. While Muchova beat Osaka on clay in Madrid last spring, the Czech was contesting her first tournament since the US Open this week after being sidelined with similar abdominal problems. Osaka next faces American Alison Riske, who defeated Ann Li 6-2, 3-6, 6-3 in an all-American clash. In Round 2, Muchova defeated reigning US Open finalist Leylah Fernandez, while Osaka took down Angelique Kerber in a clash of Grand Slam champions. Lucky loser Lucia Bronzetti of Italy also moved through to Round 4 via a walkover as Anna Kalinskaya withdrew thanks to a left arm injury. Bronzetti will next face wildcard Daria Saville of Australia. Saville also had abridged passage through to the last 16, as Katerina Siniakova retired after losing the first seven games. The former Top 20-ranked Australian, on the comeback trail following Achilles surgery, also reached the fourth round in Indian Wells as a qualifier, while Bronzetti, ranked World No.102, is amid a breakthrough in her first WTA 1000 main draw. /IANS