The 2026 ATP and WTA seasons begin with the opening day of the United Cup. Naomi Osaka’s Team Japan will face Stefanos Tsitsipas’s Team Greece in Perth, after Team Spain’s tie with Team Argentina. We here at LWOT predict the confirmed matches in this article, but which players do you think will win?

United Cup Day 1 Predictions
Jaume Munar vs Sebastian Baez

Head-to-head: Baez 1-0 Munar

Munar is generally the more comfortable of this pair on hard courts, despite Baez’s title in Winston-Salem just over two years ago. The Argentine will try to bring his powerful forehand into play consistently. If the conditions are similar to previous years in Perth, that will favor Munar more. He is slightly favored in a contest that will contain several lengthy rallies.
Prediction: Munar in 3

Jessica Bouzas Maneiro vs Solana Sierra

Head-to-head: Bouzas Maneiro 1-0 Sierra

Both women grew up on clay, and it remains their favored surface. However, Bouzas Maneiro is more accomplished on other surfaces and has more firepower. Sierra is a fighter, but she can only win if her higher-ranked opponent underperforms. I think Bouzas Maneiro will prevail, and, if Munar also triumphs, give Spain an unassailable 2-0 lead before the doubles.
Prediction: Bouzas Maneiro in 2

Embed from Getty Images

Stefanos Tsitsipas vs Shintaro Mochizuki

Head-to-head: First meeting

A strong start to 2026 feels particularly important for Tsitsipas. Question marks surround the 2023 Australian Open runner-up after a poor 2025 and persistent back issues. If the Greek is unsteady from the baseline, Mochizuki’s usual consistency will make this a challenging match. Tsitsipas’s past results in Australia make me back him, but that is not with complete confidence.
Prediction: Tsitsipas in 3

Naomi Osaka vs Maria Sakkari

Head-to-head: Osaka 3-2 Sakkari

Osaka finished 2025 impressively under Iga Swiatek’s former coach, Tomasz Wiktorowski, with final and semifinal runs at the National Bank Open and the US Open. At her best, the four-time Grand Slam champion’s powerful game will overwhelm Sakkari, who struggles against pace. Sakkari’s inconsistent past couple of years are another reason not to be optimistic about her chances.
Prediction: Osaka in 2

Main Photo Credit: Mike Frey-Imagn Images