A GUEST appearance by Britney Spears gave the CBS sitcom “How I Met Your Mother” its highest viewership of the season Monday, and assures the modest performer will be renewed for a fourth season in the fall.

“Mother” pulled in about 10.6 million viewers, a huge spike from its season-to-date average of 7.8 million, according to Nielsen Media Research.

Critics were relatively impressed. “Spears proved she can act every bit as well as she can sing,” wrote the New York Daily News. “Brit looked slim, (OK she was behind a desk), trim and gorgeous,” wrote the New York Post.

Spears, whose professional achievements have been engulfed by an avalanche of marital, health and legal woes in recent years, played a dermatology office secretary named Abby. She said in a statement issued two weeks ago, while shooting her scenes, that she was having “a blast.”

“How I Met Your Mother,” narrated through flashbacks from the future, stars Josh Radnor as a man who is joined in his quest for true love by his lecherous pal, played by Neil Patrick Harris. (SD-Agencies)