Danny Garcia staggers Amir Khan for a TKO

LAS VEGAS — A slew of Brits invaded Mandalay Bay here Saturday to cheer on their native son, Amir Khan, in his much-ballyhooed (and HBO-televised) junior-welterweight title unification bout against unbeaten Danny Garcia.

But, like Khan, they were blindsided in the third round when the scrap-metal-tough Garcia threw a thunderbolt left that knocked Khan’s chances of winning deep into the desert night.

Khan hit the canvas, stumbled to uncertain feet, and Garcia, of Philadelphia, felt his constituents roar and surge to their feet as he charged.

The bell soon rang, rescuing Khan, but early into the fourth, Garcia kept charging, dismantling the Brit, blow by blow. At 2 minutes 28 seconds of that round, shortly after Garcia connected with a fierce left hook to Khan’s head, referee Kenny Bayless called the fight, giving Garcia a technical knockout, improving his record to 24-0 with 15 knockouts.

“I always knew I was going to win this fight,” Garcia said. “I needed a great fighter in front of me to show how good of a fighter I am — and now everyone knows. I will fight anyone, any time, anywhere.”

Khan (26-3) is the biggest notch on Garcia’s belt, a win that could boost him into the superstar welterweight division where Floyd Mayweather Jr., Manny Pacquiao and Timothy Bradley hold court.

“I told you Danny was underrated,” said Angel Garcia, his father and trainer. “I knew he was going to knock him out.”

As for Khan, who had promised a knockout, he entered the ring as a 7-1 favorite at fight time with his World Boxing Assn. title at stake, a title the WBA bestowed him three days prior without his throwing a single punch.

Khan had lost that title in a controversial split decision against Lamont Peterson last December, but Peterson tested positive for synthetic testosterone in May and admitted he started using the substance a month before he fought Khan.

The WBA then stripped Peterson of his title, and the rematch that had been set for May 19 was nixed, extending Khan’s long layoff from the ring.

His break stood at more than seven months by Saturday, a boxing hibernation that he didn’t anticipate but one he appreciated, saying earlier this month that it gave him more “power, strength and explosiveness than I’ve ever had before.”

But Khan said after the fight that he came in with his hands down and that Garcia, who was in his first fight defending his World Boxing Council title, took advantage.

“I respect Danny,” Khan said. “He was countering very well against me. I got a little complacent and he took advantage and he caught me.”

Khan added: “I was a little surprised the ref stopped it. I thought he was going to let us continue. My mind was clear and I thought my legs were OK.

“But I respect the judge, the ref and the commission for the decision.”

baxter.holmes@latimes.com