PERTH, Australia — World No. 3 Coco Gauff went straight to business in her 2026 season debut at the United Cup, helping the defending champion United States earn a 2-1 win over Argentina in Group A on Saturday.

Argentina struck first when Sebastian Baez delivered one of the best performances of his career, upsetting World No. 6 Taylor Fritz 4-6, 7-5, 6-4 to open the night session and give Argentina a 1-0 lead.

Gauff responded by defeating rising star and No. 66 Solana Sierra 6-1, 6-1 in 57 minutes to level the tie at 1-1. That result sent the tie to a deciding mixed-doubles match.

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Gauff then teamed with Christian Harrison to close out the match, earning a 6-4, 6-1 win over Maria Lourdes Carle and Guido Andreozzi. They controlled the match from the baseline, were assertive at the net and wrapped up the victory in 63 minutes, giving the United States a 2-1 win. The U.S. is now 1-0 in Group A and will next face Spain.

“It was fun, I’ve watched Coco play so much and I’m such a big fan,” said Harrison, who said he was playing for his country for the first time. “It’s just fun to share a match like that with these guys, some people that I look up to, and it’s good to just get out there and enjoy playing hard.”

Argentina’s quarterfinal fate will be determined by its showdown against Spain. Gauff is scheduled to face Spain’s Jessica Bouzas Maneiro on Jan. 5.

It was the first encounter between Gauff and Sierra on the WTA Tour Driven by Mercedes-Benz, and Sierra’s first career Top 10 matchup.

“I feel like I can play even better, too, which is even more exciting,” Gauff said on court after the match. “It’s always tough starting the first match of the season, especially against an opponent like her and someone who played yesterday. I’m really happy with how I managed all those emotions.”

Gauff raced to a 5-0 lead behind a pair of breaks and three strong service holds, saving two break points along the way. Sierra earned a loud response from the Perth crowd when she held in the sixth game, before Gauff closed the set in 30 minutes while limiting Sierra to just seven points on serve.

The second set followed the same pattern. Gauff, who went undefeated in singles at last year’s United Cup, closed out another 6-1 set to complete the win.

“I definitely think there’s things I can do better from being hyper critical, but it’s a straightforward win,” Gauff said to reporters. “I think as the more the season goes, I feel like that stuff will settle in even more.”

Baez, meanwhile, earned his second career Top 10 victory and his first win over Fritz after five previous losses. The No. 45 player in the PIF ATP Live Rankings rallied from a set and a break down and saved a break point while serving for the match at 5-4 in the third set before sealing victory with a volley into the open court.

“I am so happy right now,” Baez said on court. “We have been searching for this feeling for many years, and I am happy to give this point to Argentina. Thank you to the crowd. I felt very comfortable today.”

Baez had defeated Spain’s Jaume Munar in his opening match Friday. Argentina defeated Spain 3-0 in its first Group A tie.