Garbiñe Muguruza and Petra Kvitova picked up victories in their clay-court season debuts at the Volvo Car Open on Tuesday.

No.6 seed Muguruza earned her tour-leading 21st match-win of the season with a 6-1, 6-3 win over qualifier Magdalena Frech.

No.3 seed Kvitova followed on Althea Gibson Court with a 7-6(4), 6-2 victory over qualifier Storm Sanders.

Muguruza won a 70-minute match against Frech in the Spaniard's long-awaited return to Charleston. The former World No.1 had only played the tournament once before in 2013, where she fell in the first round to Jessica Pegula, who was a qualifier at that time.

This time around, Muguruza would notch her first-ever victory at the tournament (after a first-round bye this year) by staving off both of the break points she faced and slamming 24 winners, four times the total from Frech's racquet.

"I’m happy that I got this win, that I fought hard, that I kept my fighting spirit through the whole match, also in the second set which was tighter than the first set," Muguruza told the press, after the match. "I’m pleased with that, very simple."

2021 Charleston 500 Highlights: Muguruza eases past Frech into round of 16

2021 Charleston 500

World No.159 Frech picked up her first tour-level main-draw win of the season over fellow qualifier Grace Min in the opening round, but the 23-year-old from Poland saw her run end at the hands of Muguruza, as she fell to 0-4 against Top 20 opponents.

With great depth and powerful precision, Muguruza took control of the first set, regularly following her big shots into the net for putaways. Muguruza obtained an early break for 3-1 after a blistering backhand set her up for a winning volley, and she claimed a second break with a backhand crosscourt winner, opening up a 5-1 lead.

Serving for the set, Muguruza faced break points for the first time all day, but the Spaniard powered her way out of trouble and held for the one-set lead. Muguruza had 11 winners in the opening frame, well outpacing Frech’s three.

Frech picked up her groundstroke play to keep the early stages of the second set competitive, but Muguruza at last wrested control there as well, punching an overhead winner on her fifth break point of a protracted game to break for a 4-3 lead.

Muguruza ultimately knocked off the final four games of the encounter to collect the victory and set up a clash with No.11 seed Yulia Putintseva in the round of 16. Putintseva breezed past her fellow Kazakh Zarina Diyas, 6-2, 6-2, also on Tuesday.

Kvitova was also contesting the Volvo Car Open for the second time in her career, and she needed 86 minutes to win her first-ever match at the event (following a first-round bye). In her only prior appearance in Charleston, Kvitova lost to fellow Czech Kristyna Pliskova in her opening match in 2018.

Two-time Wimbledon champion Kvitova had to grit her way through a closely-contested first set before easing past World No.187 Sanders of Australia in the second set, but Kvitova never faced a break point in the clash despite the initial parity.

Kvitova had a chance to take control of the first set after a return winner gave her a break point at 3-3, but Sanders withstood the charge by the powerful Czech and stayed on serve. Strong serving by both from that point forward caused the pair to move inexorably into a decisive tiebreak after 47 minutes of play.

An early Sanders minibreak was erased as the duo moved to 4-4 in the breaker, and after a missed forehand and a wide return that clipped the netcord, Sanders had ceded a 6-4 lead and two set points to Kvitova. The Czech took advantage right away, cracking a forehand winner crosscourt to close out the set.

The second set was broken open early as Kvitova broke serve with deep returning to take a 4-2 lead. Kvitova rolled on from there, as she clinched the last four games of the encounter to move into the round of 16.

In the final first-round match of the tournament, No.14 seed Coco Gauff breezed through Tuesday's nightcap with a 6-3, 6-0 victory over Tsvetana Pironkova.

Gauff, 17, needed just 72 minutes to oust the resurgent Pironkova and line up a second-round clash with Russia's Liudmila Samsonova on Wednesday.

Gauff, who won the Roland Garros junior singles title in 2018, is entered in just the third WTA clay-court event of her career.

"I like sliding, and I’m a pretty good mover on hardcourt, so I think it translates to clay," Gauff said in her post-match press conference. "Especially with the sliding, I feel like I move a little bit quicker on clay, because you don’t have the hard stops, and you’re able to elongate your steps. Clay gives me a little bit more time to prepare my shots, and I don’t feel as rushed on the clay."

Pironkova trimmed a 4-0 lead to 4-3 before Gauff knocked off eight straight games in a row to seize victory. Gauff won nearly 80 percent of her first-service points while also converting six of her 13 break points.

"I played pretty well, and when it got close in the first set, I was able to control the points, find my calmness, and pull through," Gauff said.

Another American teenager also won a night-time first-rounder on Tuesday as 19-year-old wildcard Emma Navarro beat Renata Zarazua 6-4, 6-3.

The Charleston native Navarro, who reached the 2019 Roland Garros junior singles final, converted five of her six break points in the match to upend Zarazua in an hour and a half, clinching the first WTA main-draw match-win of her career.