Last year's champion Garbiñe Muguruza opened up her title defense Tuesday at the Dubai Duty Free Tennis Championships with a tricky 7-6(5), 2-6, 6-2 first-round win over Czech qualifier Katerina Siniakova.

No.4 seed Muguruza won the topsy-turvy affair in 2 hours and 24 minutes, leveling her head-to-head with 45th-ranked Siniakova at two wins apiece.

"We always play very difficult matches, and today I was ready for it," Muguruza said afterward. "I think the first set was the key, it was such a tough set. In the second set, she came [back] playing better. I’m happy that I won this match, all of these matches are important."

Fast facts: World No.7 Muguruza won the first of her three 2021 titles in Dubai last year, besting then-surprise finalist Barbora Krejcikova in the championship match.

But in her eighth consecutive appearance at the tournament, former World No.1 Muguruza needed to work hard to extend her 2022 campaign beyond her opener versus Siniakova, who is Krejcikova's compatriot and doubles partner.

Siniakova, the No.1-ranked doubles player on tour, was seeking her eighth career singles victory over a Top 10 player, and had beaten Muguruza in their past two meetings, including in Montreal last year.

But Muguruza was able to prevail despite converting only four of her 18 break points. Muguruza was highly successful returning the Siniakova second service, winning exactly two-thirds of those points.

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Key moments: Siniakova had a significant lead in the opening frame, reaching set point as she served for the first set at 5-3. However, the Czech double-faulted away that chance, and Muguruza pulled back on serve after Siniakova double-faulted again on the Spaniard's seventh break point of that grueling game.

The first-set tiebreak was closely contested but Muguruza earned her first set point with an ace to lead 6-5. Muguruza converted that chance when Siniakova netted a backhand after nearly an hour and a quarter.

The momentum swung as Siniakova took charge of the second set right away. Siniakova found a forehand winner in the corner to break Muguruza at love in the first game, then fended off a break point to consolidate for 2-0. Siniakova was never broken in the second set as she leveled the match.

In the final set, though, it proved to be Muguruza’s day as she slammed an ace to hold for 3-2, then used a deep return to break Siniakova and lead 4-2. Muguruza was forced to stave off two break points in the next game, but she held on, capturing the final four games of the match.

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Next up: Muguruza will take on Veronika Kudermetova of Russia in the second round. Kudermetova dispatched former World No.1 and 2010 Dubai finalist Victoria Azarenka in straight sets earlier on Tuesday. Muguruza leads Kudermetova 3-0 in their head-to-head.

Sabalenka seals victory over Kostyuk

No.1 seed Aryna Sabalenka of Belarus was the last player to claim her spot in the second round, winning the late-night match over 19-year-old Marta Kostyuk of Ukraine 6-4, 6-1.

World No.2 Sabalenka battled through a topsy-turvy opening set but righted the ship in the second set, emerging with a 1-hour and 15-minute win over 49th-ranked Kostyuk.

Highlights: Sabalenka def. Kostyuk

"It was a tough match, she played really well," Sabalenka said on-court, after her victory. "I fought so hard for this win and I’m really happy with the result."

In her first match since a Round-of-16 loss to Kaia Kanepi at the Australian Open, Sabalenka refused to come unglued by her nine double faults. Sabalenka won nearly 80 percent of points returning the Kostyuk second serve, breaking the teenager seven times.

Jimmie48/WTA

After Kostyuk held serve in the opening game of the tilt, six straight games went to the returner before Sabalenka stopped that streak with a hold for 4-4. Sabalenka's powerful game then took command in the latter stages, as she ended up winning the last four games of the set.

A screaming return winner gave Sabalenka the first break of the second set at 2-1, and despite facing three break points at 4-1, the top seed did not drop another game.

Sabalenka is now one win away from a third straight trip to the Dubai quarterfinals. She fell to eventual champion Muguruza in the elite eight last season.

To get there again, she will have to defeat another power player, two-time Wimbledon champion Petra Kvitova, in the second round. Sabalenka and Kvitova have split their four meetings, but they have not faced off since Sabalenka defeated Kvitova in the Doha final two years ago.