Grand Slam champions Bianca Andreescu and Sofia Kenin sealed safe passage through to the third round of the Miami Open as day turned to night on Friday.

In her first match in five weeks, 2019 US Open champion Andreescu twice trailed by a break in the opener and saved two set points before securing a 7-6(5), 6-2 win over Czech qualifier Tereza Martincova in one hour and 52 minutes.

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"I felt really good mentally out there. That's the one thing I feel like I was struggling a little bit in Australia, but I was just super positive and I fought for every ball no matter what the score was," Andreescu said after the match.

"In the first set she had set point, but I just kept fighting, and I think that was the thing I was most proud of. I felt that in the first set I wasn't as consistent as in the second set, but I think that tiebreaker really said a lot, because I started putting more pressure. I was getting to a lot of balls.

"In the second set, you could tell that she became a little discouraged, and she started going for more shots. But that's part of my game style. I want to be very physical out there. I don't want to let any ball go and just never give up. I think that says a lot today in the match, and it showed."

2021 Miami Highlights: Andreescu maneuvers past Martincova

Andreescu will next face No. 28 seed Amanda Anisimova, who overcame Sloane Stephens in an all-American second round encounter, 6-3, 6-3. Peers in the juniors, Andreescu and Anisimova have never played on the professional tour. 

"I practiced actually with her the other day. I didn't know I was playing her. But I think it's going to be a great match," Andreescu said.

"She hits very flat, so I have to be ready for everything. She has a very good serve, but I'm feeling good out there and I think it's gonna be a very good match."

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Elsewhere, 2020 Australian Open champion Kenin, playing her first match since an appendectomy that concluded her stay in Australia, rallied from a set down to beat former Top 10 player Andrea Petkovic, 6-7(6), 6-1, 6-3.

After posting a 3-3 record in Australia, losing out in the second round of her title defense in Melbourne to Kaia Kanepi, Kenin rallied for victory in her first match on home soil in six months in one minute short of two hours. 

"I'm obviously happy with this win. It feels nice to get the win after some time not being on court, playing at tournaments," Kenin told reporters after the match.

"It was very humid. I'm obviously used to this since I live here, but conditions weren't so easy, but I'm happy that it wasn't at least windy. I was able to somehow try to play my game.

"I felt a bit more nervous at the beginning, first match after having the surgery and everything. I just told myself, 'Keep fighting.' I'm just grateful that I'm able to play here because I really wanted to get ready for the Miami Open and just try and enjoy every minute out there."

Rounding out the night session, in-form Spaniard Sara Sorribes Tormo scored her 10th win in her last 11 matches with a 3-6, 6-4, 6-1 comeback victory over Australian Open finalist and No.13 seed Jennifer Brady.

The Guadalajara champion earned the three-set victory in two hours and 22 minutes, the ninth time she has played more than two hours this year. 

"I think today was one of the best matches I played. I'm 100% sure. I don't want to say it's the best match I played, but I'm sure it's one of the best," the Spaniard said after the match.

"It was difficult because she's a really good player. I think she started really well the match. I think I didn't start that well, and the second set, everything was very close. I'm proud of working all the match. [I didn't] stop fighting. I stayed there no matter what, no matter the score. I'm just super happy about that, because I think that's something I need to do. I have to fight until the end."