Fortunately for them both, Bruce happens to be fuck mothering Batman, so when Rachel lets go of her shadowy hand-hold and falls the rest of the way down, he's able to catch her without incident in that obnoxiously perfect Hollywood-impossible style, with barely a stagger.

Still, he makes a little 'oof' noise for comedic affect.

"You should carry a flashlight," he observes, hair still slightly screwed up from the windforce of her fall very near his head.

In other words: neat trick.