Barney and Britney — together again.

So tonight we found out that a little Britney Spears goes a long way. It’s not that she bombed in her return engagement on “How I Met Your Mother.” It’s just that she had a larger role and the strain showed.

When the pop singer appeared on the show a few weeks ago, it was all novel and sweet and fun. And her bit role as an office receptionist goosed the ratings enough to warrant a return, despite the protests of Neil Patrick Harris.

Tonight, she was given more to do as her character, Abby, slept with Barney to make Ted jealous. And then, in a bid up the ante, Barney issued a fake proposal to Abby (in front of Ted), only Abby is convinced it’s genuine. That all led to one of the best lines of the night as Britney/Abby tells Barney she was considering a Fourth of July wedding, but “but I didn’t want to steal any attention away from America.”

This time, Britney’s character came off as more ditzy than sweet and several times her delivery just felt a little flat. Then again, for me, maybe it’s just that the thrill is gone.

But Britney probably isn’t. Her final scene tonight had her Abby considering a another run at Ted (with Barney’s encouragement), which means the door has been left open for at least one more guest stint. We’re guessing November sweeps.