Jeff Bezos, Lauren Sánchez Hit Up UFC 306 At Las Vegas Sphere

The UFC did not disappoint with the first-ever sporting event at The Sphere in Vegas ... and Jeff Bezos' fiancée, Lauren Sánchez, was right there chronicling the whole amazing night.

Lots of celebs hit up UFC 306, including Chris Brown, Taylor Lewan, Andrew Schulz, Bob Iger and Shannon Sharpe.

Of course, Jeff and Lauren sat cage-side -- seats were SUPER expensive, but they scraped up enough dough -- as she pulled out her cell phone and sprayed the venue with video for her followers.

It's an amazing feat to pull off ... UFC honcho Dana White hatched the plan when he hit up the U2 concert for the big opening, but there were huge obstacles ... not the least of which was keeping the fighters from getting distracted by all the lights. He explained his plan Friday on "TMZ Live."

The event -- "Noche UFC" was what Dana called his "Love letter to Mexico." It was supposed to cost the UFC $8 mil to produce, but it ended up costing $20M. The typical cost when the event is held at the MGM Grand is just north of $2 mil.

Big, surprising main card finish -- Merab Dvalishvili beat Sean O'Malley by decision on the main card. It was Sean's second loss.