John Mayer in concert at the John Labatt Centre last night. (Mike Hensen, Sun Media)

LONDON - John Mayer was the hot headliner at the John Labatt Centre last night -- but there was just as much buzz about Jessica Simpson being in the house.

That's how celeb coupledom works. It is hottest when there is a sighting of the twosome together, even when it's just for a wave and a smile.

Music and Mayer first. The U.S. singer-songwriter rocked and soothed and smoothed his way to standing ovations from the 6,200 mostly young fans during his show.

He opened with a great version of Belief, one of his sharpest social activism songs, and ended the show about 90 minutes later, after a blues jam that gave the two other guitarists in his fine band room to stretch out along with the star.

I think he was better -- sharper edged, bluesier and wittier -- than on his trip to the downtown London arena in 2003. Can't say if it was because Simpson was in the house.

It can't hurt having a beautiful romantic partner drop by a tour stop in Canada. Simpson apparently did not see the shows in Toronto or Ottawa.

Simpson and Mayer entered the downtown arena to cheers and screams from fans about 30 minutes before he hit the stage. Some of the fans had been waiting since 2:30 p.m. and had seen the couple come and go a few times. Most of their time was spent in a tour bus.

"Fans were screaming her name and so she turned and said 'Hi' and then they went in," said one fan, a 30-year-old woman from Cambridge who was seeing her sixth Mayer concert.

Simpson's presence was confirmed by centre representatives, but no interview could be arranged. She was expected to fly out of London last night.

Simpson had played a little table tennis during the afternoon before taking in the terrific show by Mayer -- and how can those celeb websites call him her "borefriend" -- from a private location.

There is always going to be a short supply of singer-songwriters who can speak about their generation and play brilliant and supple guitar and jump around in a perfect goofy dance while reminding those of an older generation of Curtis Mayfield and the Impressions.

That would be the effect of the anthem Waiting on the World to Change, Mayer's hit single off Continuum (Columbia/Sony BMG).

Then, there are not too many blues guitar aces who can write a sexy, lovely love song like Your Body is a Wonderland. Mayer wrote it when he was 22. He turns 30 later this year and has made sure his signature song has grown along the way.

Last night, Wonderland was a beautiful way to start an encore because it was a song the fans had been waiting for all night. Mayer came up with a duo unplugged arrangement, using a second guitarist to play bluesy steel licks.

His guitar playing, his falsetto, his command of the blues and his lyrics were all known quantities.

What this reviewer didn't know was the man can tell a celeb joke, too. Apparently, Mayer loves to test people by getting them to admit they've seen a non-existent Al Pacino movie called Freezing Point. Its big line is supposed to be: "You're getting colder."

Could have fooled me, John. Last night, you -- and Jessica -- were hot. You can heat up London any time.