I feel like the tension can be "the sex" if deployed well. Another component I think serves as "the sex" that we must be getting to fast are details and dialogue. Lingering on what someone is wearing even if they're going grocery shopping is a good example, if the encounter depends on grocery shopping, of course. You can also have a character thinking dirty thoughts of anticipation while building up the world and workaday detail.
If I'm working on a vignette and feel the need to "get to the sex" quickly, I usually just straight up start with a sex act, and if necessary, have it functioning as a flashback. For example, I once wrote a story that was about a college football team getting put on probation because it was throwing sex parties for its recruited athletes. Rather than build up with the investigator's personality or background (a woman whose desires were co-opted by her brushes with the team, its coaches, and the cheerleading staff) I started with the description of an orgy — which had been captured on a tape that was sent anonymously to the investigators' offices. So the main character and her partner watch it, share some expository dialogue about what's going on, the reader gets the fucking and sucking in obscene detail, and we've moved the story along to a point where we can do non-sexy things to round out the characters and their journeys.
