Familiarity is hardly a negative in melodrama, however, where its very predictability can be as comforting as a favorite blanket. “One Day,” which opens Friday, understands the role it plays, but it’s smarter and more polished than many of its ilk — and it soars on the appeal of its leads.

Adapted by David Nicholls from his best-selling novel, “One Day” follows Emma (Anne Hathaway, “Love and Other Drugs”) and Dexter (Jim Sturgess, “21”). We begin in 1988 as the two, drunk and having just graduated from college in Scotland, hook up for a somewhat shaky one-night stand.

So begins a friendship that endures in spite of pronounced differences. Emma is idealistic, but insecure and vulnerable. She drifts from waitressing to teaching, and falls into a relationship with a would-be comedian (Rafe Spall, “Hot Fuzz”), the requisite nice guy who’s wrong for her. Dex is charming, but callow and arrogant; he becomes a TV dance-party host who lets fame go to his head.

These are archetypes, of course, but “One Day” is so deftly executed, from Rachel Portman’s lush musical score to Benoît Delhomme’s sundappled cinematography, you just might forget that you’ve seen this all before. And director Lone Scherfig (“An Education”) wisely gives her top-notch cast plenty of berth.