LONDON — Alexander Zverev ascended to the world No. 1 ranking in men's professional tennis on Monday, becoming the 30th player to reach the summit and the oldest first-time No. 1 in 52 years. The German secured the top spot after Jannik Sinner withdrew from the season due to inflammation in his right knee, with Zverev's ascent confirmed after he reached the quarter-finals at the Vienna tournament. Zverev, 29, captured his first two Grand Slam titles at the French Open and US Open this year, ending years of frustration in major finals. At the French Open in June, Zverev beat Flavio Cobolli in the final for his maiden major championship. At the US Open in September, he defeated Ben Shelton to claim his second major title. The German also reached the final at Wimbledon, losing to Jannik Sinner, and the semifinals at the Australian Open. Zverev finishes the season with a 65-17 record. He joins Boris Becker as the second German man to reach No. 1. The ATP confirmed Zverev will finish the season as No. 1. In addition to his Grand Slam titles, Zverev's career includes an Olympic singles gold medal, two ATP Finals titles and seven Masters 1000 trophies. Zverev was diagnosed with Type 1 diabetes at age 4. Abuse allegations from two ex-girlfriends surfaced ahead of his ranking ascent, with one resolved following an agreement between German prosecutors and his former partner, and the ATP investigating another case in which insufficient evidence was found.