NEWPORT BEACH, CA, USA -- No.6 seed Sachia Vickery of the United States kept her hopes of winning the biggest title of her career alive on Thursday, as she advanced to the quarterfinals of the Oracle Challenger Series event in Newport Beach with a victory over Sweden's Rebecca Peterson, 6-1, 6-4.

After the first round of the WTA 125K Series event saw all of the Top 5 seeds eliminated, Vickery is the highest-seeded player remaining in the draw. The American overcame Peterson with solid serving, hitting three aces and getting 74 percent of her first serves in, en route to a straight-set win.

Read more: Collins survives a tough day for Americans at Newport Beach

The Swede had her chances, holding nine break points in the match. Two of those were in the final game of the opening set, and Vickery needed four set points before taking the one-set lead.

Peterson could only break Vickery once in the match, to tie the second set at 2-2, and the Swede dropped serve in the next game to hand back the decisive break lead. Vickery again struggled to close out a set, having to fend off another break point and needing three match points before finally moving through in 82 minutes.

The only other seed left in the draw also rolled into the quarterfinals on Thursday, as No.7 seed Ajla Tomljanovic of Croatia dispatched Canadian Carol Zhao, 6-1, 6-3, in one hour and four minutes. Tomljanovic had four aces and broke Zhao's serve six times during the match.

Two more players won through on Thursday to complete the quarterfinal slate. American Nicole Gibbs defeated Anna Karolina Schmiedlova of Slovakia, 7-6(6), 6-4, and Jil Teichmann of Switzerland ousted American wild card Victoria Duval, 6-4, 6-2.

In the top half of the draw, Gibbs will take on Tomljanovic in one quarterfinal, while American wild card Danielle Collins will play Jang Su Jeong of South Korea in another. The quarterfinals in the bottom half have Vickery going up against Japanese qualifier Mayo Hibi, and Teichmann battling Russian qualifier Sofya Zhuk.