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.
In the New York Post, Linda Stasi wrote: "You'd never know that pop tart Britney Spears had ever had a bad day in her life.
"Now clean and sober and under her dad's thumb once again, Britney looked as adorable last night as she did waaay back when.
"On the show, which she filmed in the last few weeks, Brit looked slim, (OK she was behind a desk), trim and gorgeous.
"And, more importantly, her acting was nothing short of adorably believable.Mother was the fourth-highest-rated show of the evening, and CBS won the night (averaging 12.5 million viewers), even as the rest of its comedy lineup dropped slightly from last week's record-setting return to original episodes.
Spears, 26, played love-struck receptionist Abby in a tattoo-removal clinic who falls for the main character, Ted. Spears spent two days filming the scenes. She last made a TV appearance with a guest role in the sitcom Will & Grace in 2006. 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.
Producers said there were "no diva moments" and Josh Radnor, who plays Ted, told USA Today the cast tried to provide "a nice safe place" for Spears.
"It's a cute, funny role, and she ended up being great in it," he said.
"She's actually very vulnerable and sweet."
He went on: "We both screwed up our lines (during taping) and made fun of ourselves.
"She definitely has comedic instincts. She made funny line readings (during script read-throughs). That's the sign of a good comedic actor."
However, it had been claimed her co-stars struggled to work with her because she refused to take off her sunglasses until the cameras started rolling.
A show insider told the National Enquirer magazine: "Britney delivered her lines, but the show's actors had a tough time reading her expressions since they couldn't see her eyes at all.
"It's hard for an actor to make a connection when all he sees is his own reflection staring back at him in shiny dark glasses, but no one wanted to upset Britney by asking her to take them off.
"In the end, someone said to her, 'You will be taking the sunglasses off for the actual tapings, right?' To which Britney responded, 'Uh ... yeah!'"
How I Met Your Mother is shown on the Seven Network in Australia.
Meanwhile, Spears's life remains in the hands of her father Jamie, after a claim challenging his conservatorship was rejected yesterday.
Jon Eardley - who claims the troubled singer hired him to challenge Jamie's control of her estate and daily life because it violates her civil rights - filed a claim in the Los Angeles Court of Appeals, but the judge rejected it without even seeking a response from Jamie and co-conservator Andrew Wallet.
While Spears's team have always denied the 26-year-old asked Eardley to represent her, the lawyer has now produced a transcript of a phone conversation they had before Jamie was made responsible for his daughter.
In the call, Spears - who set up the call through a paparazzo friend and speaks in an English accent throughout the conversation - can be heard saying: "Basically I want my life back. I want to drive my car. I want to live in my house alone. I want to pick my own security, see who I want to see and make it happen."
