As supporting characters, married couple Pete (Paul Rudd) and Debbie (Leslie Mann) earned a heap of screen time in the acclaimed 2007 comedy “Knocked Up.”

Debbie was even the centerpiece of one of the decade’s funniest scenes, when she couldn’t get into a dance club because she was too old.

Age again factors in for the pair, who now enjoy top billing in the pseudo sequel “This Is 40.” The result is a hilarious, unflinchingly candid look at the woes of an ongoing marriage between people who are “like a magnet for negativity.” It delivers the most laughs of any comedy this year.

The alternately meek and combative Pete is fresh off launching his own record label, but the move is proving shaky. He keeps signing older performers he personally enjoys — such as New Wave relic Graham Parker — instead of ones who sell.

As his marketing chief Ronnie (Chris O’Dowd from “Bridesmaids”) expresses, “It’s hard to watch a band when they all remember V-Day.”

At home, Pete resorts to popping Viagra to keep things “turbo-charged” in the bedroom. This does nothing to bolster Debbie’s self-confidence, especially since she, like her husband, is facing her 40th birthday (though she insists it’s her 38th).

The scolding, health-conscious Debbie is also reminded of her own mortality at the clothing boutique she owns, comparing herself daily to a buxom employee (Megan Fox) who might be guilty of stealing from the struggling store.

The couple’s marital and economic strains are filtering down to their children. Teen Sadie (Maude Apatow) is infatuated with the unfulfilling TV drama “Lost.” Young Charlotte (Iris Apatow) is feeling shunned by a sister growing too old to play with her.

Pete retreats from the household drama by pretending to use the bathroom when he’s really just sitting on the toilet playing video Scrabble.

“Why is your instinct to escape?” Debbie grills him.

It’s hard to describe “This Is 40” as actual escapism, despite its nonstop humor. The relationships are simply too authentic. The arguments too recognizable. The tension alarmingly tangible.

Writer/director Judd Apatow exploits the advantage of casting his wife (Mann) and daughters — all of whom are terrific. How many of these conversations really took place before Apatow transformed them into a screenplay? It sure feels like plenty. Rudd (who was raised in Overland Park and attended KU) fits into the family dynamic perfectly. Few actors are better at playing a nice guy who is equal parts frustrating.

The story reaches a crescendo at the feared birthday party. This setting provokes a batch of confrontations, which also involve Debbie’s wealthy absentee dad (John Lithgow) and Pete’s needy dad (Albert Brooks) — both men are remarried and have younger children. The actions by these patriarchs don’t justify Pete and Debbie’s personality foibles; they merely explain them.

“This Is 40” is admittedly episodic and runs a tad long given its genre. It’s thin on plot, yet thick with perspective.

It’s also deliberately messy. Don’t expect a comfy romantic comedy. This husband and wife appear incapable of sincere compromise. Their problems don’t get tidily resolved, and their conflicts don’t evaporate.

Pete and Debbie are who they are, and it’s clear that’s all they’re ever going to be. The question is whether they can remain OK with that situation.

WHAT OTHERS ARE SAYING

•  Colin Covert, Minneapolis Star Tribune: “A bull’s-eye zeitgeist comedy, a movie in which everyone acts like real people but funnier. … Wise and satisfying, and often sharp and hilarious.”

•  Peter Travers, Rolling Stone: “Apatow is an expert at spotting the fissures in a relationship. That’s what makes ‘This Is 40’ so potently, painfully funny, even when it’s gross.”

•  Dana Stevens, Slate: “At its worst, ‘This Is 40’ feels like being condemned to watch two hours of someone else’s home movies — overly long, self-indulgent and bone-crushingly banal.”