But two of the world’s top 10 crashed out as Americans Taylor Fritz and Ben Shelton lost to French duo Corentin Moutet and Arthur Rinderknech respectively.
Alcaraz, back on grass for the first time since winning his second Wimbledon title last year, beat his 86th-ranked opponent 6-4, 7-6 (7/4) on a sweaty day in west London.
The Spaniard, who overcame Jannik Sinner in a five-set thriller at Roland Garros just nine days ago, broke in the seventh game and went on to clinch the first set against lucky loser Walton, who replaced Alejandro Davidovich Fokina after he withdrew due to illness.
The 2023 Queen’s champion appeared to have found his rhythm only for Walton to rally impressively, carving out two set points on his opponent’s serve in the 10th game.
But the Australian failed to convert either of them and Alcaraz levelled, coming out on top in the subsequent tie-break.
“First match on grass is never easy to get used to the competition again, to get used to the grass again,” he said.
“So, I just want to say thank you for helping me a little bit.”
The world number two faces compatriot Jaume Munar in the last 16.
World number four Fritz failed to convert a match point against Moutet before losing 6-7 (5/7), 7-6 (9/7), 7-5.
Moutet held on in the second set tie-break before securing the only break of serve in the match in the final game.
Sheldon also stumbled to a shock early exit to Rinderknech in two tie-breaks 7-6 (7/5), 7-6 (7/4).
Earlier, British second seed Jack Draper dispatched American Jenson Brooksby 6-3, 6-1 to reach the second round.
The left-hander, who has previously beaten Sinner and Alcaraz at Queen’s, won 93 percent of first-serve points and did not face a break point in a dominant display.
Draper is chasing his second title on grass after winning in Stuttgart last year, and will next face Alexei Popyrin after the Australian beat compatriot Aleksandar Vukic.
“Feels amazing, no place I’d rather be,” said Draper. “We travel the world playing tennis, never get to come home or spend much time with my family but to be on this court in front of you guys, my people, my family, thank you.” (AFP)