Mr Cameron admitted having difficulty following all the rules, but said the president was giving him some tips as they watched Mississippi Valley State University play Western Kentucky University in Dayton, Ohio.
The world leaders took front row seats for the opening game in the March Madness tournament, which saw Western Kentucky storm to a 59-56 victory in the final few minutes.
During a joint interview at half time, Mr Cameron said: “I’m enjoying it. It’s fast, it’s pretty fast and furious. It’s hard to follow sometimes exactly who’s done what wrong.”
Asked if the president was helping him, Mr Cameron told CBS basketball correspondent and former pro player Clark Kellogg: “He’s giving me some tips. He’s going to help me fill out my bracket.”
Mr Obama, a keen fan of the sport, replied: “And he’s going to teach me cricket. Because I don’t understand what’s going on with that game.”
Mr Cameron said he saw “a lot of similarities” between basketball and football, but admitted the American sport was “very fast”.
On the first evening of his three-day visit to the US, he also talked of the excitement about the forthcoming Olympics in London, telling Kellogg: “We’re going to be rolling out the red carpet to the whole world. Everything is on time, on budget, all the stadia are built, everything is ready to go.
“We’re just ready to welcome a lot of people to London. My message to people is to come, come and visit, come and see the Olympics and come and stay.”
Meanwhile, Samantha Cameron was given her own special welcome to America as she joined her husband on a visit to the US.
First lady Michelle Obama spoke of the countries’ “special relationship” and she welcomed her counterpart at a mini-Olympic competition, also using the occasion to announce she will lead the presidential delegation to the opening ceremonies of the Olympics this summer.