Carlos Alcaraz of Spain, coming off a successful title defense at the French Open, endured a tough fight before defeating lucky loser Adam Walton of Australia 6-4, 7-6(4) in his opening match at the Queen's Club in London on Tuesday.

The World No. 2 was originally scheduled to face his compatriot Alejandro Davidovich Fokina in the first round, but the 28th-ranked Spaniard withdrew due to illness.

The first set against Walton was not one-sided, and the Aussie caused a bit of trouble for Alcaraz in the 10th game after earning two break points while trailing 5-4. He then served wide and hit long, however, allowing the five-time Grand Slam winner to hold and claim the set.

The second set was much closer and needed to be decided in a tiebreak. Alcaraz won the only point against serve with the extra session knotted at 4-4, before serving out and sealing the deal with a forehand winner on his first match point. He will next face Spanish compatriot Jaume Munar in the second round.

"I feel great, I feel super happy to be back on grass. It's a special surface, a special place to me," Alcaraz said. "In these nine days I have done everything – rest up, practicing, playing a match again. It has been nine great days, and I'm happy to be back here."

World No. 1 Jannik Sinner, who came up short against Alcaraz in their epic final at the French Open, started his grass-court season by sweeping past Germany's Yannick Hanfmann in straight sets 7-5, 6-3 at the Halle Open in Halle, Germany.

Sinner, the defending champion, broke his opponent in the 12th game of the first set, jumping out to a 1-0 overall lead in the match. The Italian repeated that feat in the second set to wrap up the victory.

The top seed will face Alexander Bublik of Kazakhstan next.