The 20-year-old Wimbledon champion missed the season-opening major in 2023 because of injury but is more than making up for lost time.
The No. 2-seeded Alcaraz beat Miomir Kecmanovic 6-4, 6-4, 6-0 in less than two hours Monday to open the night session at Rod Laver Arena.
He has dropped just one set en route to the last eight.
The fourth-round match between Zverev and Cameron Norrie on Monday at the Australian Open was briefly delayed when a protester threw handfuls of leaflets bearing the phrase “Free Palestine” onto Margaret Court Arena.
Play was halted midway through the third set so that the playing surface could be cleaned up, with both players asked to sit down while the situation was resolved.
Zverev won the match 7-5, 3-6, 6-3, 4-6, 7-6 (3) to advance to the quarterfinals.
The woman who threw the leaflets from the stands was escorted out.
“As soon as the behavior was identified and reported, venue security was deployed to detain the individual,” a spokesperson from Melbourne & Olympic Parks and Tennis Australia said in a statement. “The individual was subsequently evicted from the event.”
One side of the double-sided leaflets featured the phrase “Free Palestine” with further messaging that included, “While you’re watching tennis, bombs are dropping on Gaza,” and accused Australia, as an ally of Israel, of being “complicit in war crimes and genocide.”
The other side featured a map of the region currently in conflict.
Both the Palestinian and Israeli flags are banned from the Australian Open this year because of the sensitive nature of the Israel-Hamas war.
Others banned from the Melbourne Park precinct include the Belarusian and Russian flags, as well as the flag of Taiwan. Ukrainian flags are allowed at the Open.
Information from The Associated Press was used in this report.