Carlos Alcaraz and Alexander Zverev win Vienna openers

Carlos Alcaraz won his opening match at the Vienna Open on Tuesday with a straight-sets victory over Karen Khachanov, while Alexander Zverev survived four match points to beat Martin Landaluce in a marathon encounter.

World number three Alcaraz saw off the former eighth-ranked Russian 6-4, 7-6 (7/5) in their first-round meeting.

The seven-time Grand Slam champion decided to add the 500-level event in the Austrian capital to his schedule at short notice, having not competed in it since 2021.

Sidelined from mid-April to the end of August due to a wrist injury, Alcaraz has produced mixed results since his return, including a third-round exit at the Shanghai Masters in his last tournament at the start of October.

"I really enjoyed it, even though I had to run, had to fight, had to sweat a lot. We both played great shots, great points. I would say it was a great match to watch and I'm really happy about it," Alcaraz said.

Alcaraz had to dig deep against the 30-year-old power-hitter, recovering from a break down to take the first set.

In a closely contested second frame, Alcaraz prevailed in a tight tie-break with a perfectly weighted drop shot to seal the match.

The 23-year-old will next face Georgian Nikoloz Basilashvili or local player Jurij Rodionov in the round of 16.

Zverev kept alive his hopes of securing the world number one spot before the year-end with a 7-5, 3-6, 7-6 (13/11) win over Landaluce.

"(I was pushed) to the absolute limit," Zverev said. "Credit to (Landaluce), he played an amazing match."

Zverev is assured of finishing the season atop the rankings, but should he win his next encounter against either Tallon Griekspoor or Brandon Nakashima and reach the quarter-finals in Vienna, he will claim that spot from injured Italian Jannik Sinner in next Monday's updated rankings.

Zverev secured a crucial second break of the 20-year-old Spaniard's serve in the 12th game to take the opener 7-5.

But Landaluce riposted by taking an early lead in the second set and serving out to force a decider.

An even set went through to 6-5 for Zverev, and the 29-year-old managed to force two match points on Landaluce's serve but the young Spaniard held firm to take it to a tie-break.

Zverev dug in over the course of a topsy-turvy breaker, staving off four match points for Landaluce to claim the win for himself at the fifth time of asking when the world number 67 pushed a forehand wide bringing an end to a three-hour-and-five-minute encounter.