GUADALAJARA, Mexico -- Former No.1 Victoria Azarenka advanced to the Round of 16 at the Guadalajara Open Akron after top seed Paula Badosa was forced to retire. Azarenka will face No.13 seed Madison Keys next. 

Playing flawless tennis from the baseline, Azarenka built a quick 4-0 lead before Badosa got on the board. Struggling physically, Badosa called the trainer at the 4-1 changeover to discuss her options but opted to play on. After Azarenka closed out the set with an ace at 6-2, Badosa retired due to illness. 

"You never want anybody to retire, we go out here to compete and do our best," Azarenka said on the court. "It's really sad that Paula wasn't able to finish the match. I hope she recovers quickly. I'm sure we're going to have a few more matches to play, so I'm looking forward to those."

Despite the abbreviated match, Azarenka reveled in the notoriously raucous energy of the Guadalajara night sessions. 

"I heard a lot of great things in Guadalajara from last year from the Finals, that the energy was really great," she said. "That's really what kind of motivates me the most to go out there and play, so that was really nice."

Bidding to make her first WTA 1000 quarterfinal since her run to the 2021 Indian Wells final, Azarenka will face Keys on Thursday. The American advanced to the Round of 16 with a 6-3, 4-6, 6-3 win over Ajla Tomljanovic. The victory kept Keys in contention for one of the three remaining spots at the WTA Finals. 

"We haven't played in a while, so it's going to be a good match for both of us," Azarenka said. "Not expecting too many rallies there. So we'll see."

Sloane Stephens ends Belinda Bencic's WTA Finals hopes

Sloane Stephens earned her first Top 20 win of the season, defeating No.10 seed Belinda Bencic 6-4, 6-4 to advance to the Round of 16. Stephens outdueled Bencic from the baseline and kept the Swiss at bay with a strong serving performance. Winning 76% of her first-serve points, Stephens faced just two break points in the match and was broken once. In contrast, Bencic won just 57% behind her first serve. 

Guadalajara: Stephens beats Bencic for 1st Top 20 win of the season

"Obviously, Guadalajara suits my game well, and I've been playing some good tennis here," Stephens said. "I probably have the most wins on the tour in Guadalajara this season. So it's been nice for me. Obviously, I've had some good results and some good memories, so just looking forward to getting out there tomorrow."

Stephens will face No.6 Caroline Garcia next. Garcia holds a 4-1 edge in their head-to-head. Stephens' sole win came in 2014 on the grass at Eastbourne.