The pair, who will present together during the 88th annual Academy Awards, posed for a selfie together backstage after their run-through, with Garner planting a smooch on Del Toro's cheek.
Garner and Del Toro were both laid back but focused on learning their presenter lines and stage blocking.
Del Toro, 49, tipped his baseball cap to the orchestra when he got onstage, while Garner surveyed the orchestra and the photos affixed to the seats. At one point, a crew member pointed in the direction of where she'll be sitting during the show, to which the star responded, "great."
The actress, 43, and Del Toro kept up a nice rapport, chatting easily when they weren't focused on practicing lines and learning where to stand. After nailing their bit, the pair headed off-stage.
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Makeup-free Garner came to the rehearsal straight from her son Sam's birthday party, which was held at her Pacific Palisades home earlier in the day.
A source told PEOPLE that Garner and Ben Affleck reunited to celebrate Sam's 4th birthday with a superhero-themed bash just one day following the publication of Garner's revealing Vanity Fair interview.
In the piece, Garner said that her relationship with Affleck was "a real marriage" and that the actor's alleged relationship with their former nanny (which he has repeatedly denied) had nothing to do with their decision to divorce.