The royal couple was seen leaving the British Consul-General's residence in Hancock Park around 10:30 a.m. to attend a polo match at the Santa Barbara Polo & Racquet Club.
William scored four goals as his team went on to win the overall match. Shortly after, Kate, formerly known as Kate Middleton and now referred to formally as Catherine, Duchess of Cambridge, presented each competitor a blue Tiffany & Co. box with a white ribbon, and a big silver trophy to her husband's team.
The last player to the podium was William. When the crowd yelled, "Kiss!," she obliged and gave him a slight embrace and a kiss on each cheek.
The club has hosted some of the best players and matches in the world over the last century, but never for a player who one day could become king.
"It's almost a historic moment and it fits because we're celebrating our 100th anniversary," said owner Linda Walker.
William lead his fellow polo players into competition, while the duchess sat front row center.
There are 450 VIP slots, but to sit there costs $4,000 dollars a chair. That money also includes a plate at a private luncheon cooked by Giada De Larentiis, a walk down the red carpet, and possibly an invitation behind the hedges into the royal's private hangout.
There is also a $400 ticket, which includes a boxed lunch and a seat in the grandstand.
Kate was wearing a "De Gournay" silver and marble grey hand-painted chinoiserie silk dress by Jenny Packham, according to a royal spokesperson.
After the match the couple arrived at the Belasco Theatre in downtown Los Angeles, where they were guests of honor at a British Academy of Film and Television Arts dinner honoring 42 young British filmmakers. Hollywood stars like Tom Hanks were among the guests.
"When American and British talent get together, magic happens," the prince said. "Let's continue the winning formula. Catherine and I have been hugely looking forward to tonight's event."
Her Royal Highness wore a dress by Alexander McQueen. The Duchess' earrings were leant by The Queen for the occasion. The rest of her jewelry was her own.
"She may have had one of the simplest dresses on, but she was royal," said Natalie Rotman, a fashion expert. "She carried herself like nobody on that carpet did."
Experts said she packed 40 outfits for the tour.
William and Kate took a moment to meet and shake hands with fans along the red carpet. Inside, they spoke with Hanks, Barbra Streisand and Jennifer Lopez.
The royal couple arrived in Los Angeles Friday afternoon after a nine-day trip to Canada, their first foreign excursion since getting married in April.
A garden party was held in the royal couple's honor in Hancock Park. Local dignitaries including Gov. Jerry Brown and Mayor Antonio Villaraigosa, as well as celebrities such as soccer star David Beckham, welcomed the royal couple.
"William and Kate were extremely down to earth," said L.A. City Councilman Tom LaBonge. "Spent time talking, chatting, and then you would watch them in the backyard kind of work the room. They listened to everybody and made conversation. It was a very special evening."
Several fans lined up outside of the Hancock Park home to catch a glimpse of the couple on their first trip to L.A.
"We grew up with them," said Fremont resident Anna Cruz. "When his mother and father got married, when he was born, and I just wanted to be here to give them a warm welcome to America and say that we support them."
On Sunday the couple will visit with the city's homeless, followed by attending a job fair for returning U.S. servicemen and women.
Though Prince William has been to America before, it is Kate's first trip to the U.S. William's late mother, Princess Diana, who would have turned 50 this month, charmed Americans when she visited in the 1980s.
Timeline of Prince William and Kate's visit:
Saturday, July 9
- Noon - 5 p.m. PT: Prince William played in a polo match in Santa Barbara
- 6:30 p.m. - 7:30 p.m. PT: They arrived at Belasco Theatre in downtown Los Angeles for BAFTA event
Sunday, July 10
- 11:30 a.m. PT: Royal couple arrives in Skid Row to meet with kids at Inner City Arts
- 1:15 p.m. PT: They arrive at the Service Nation event at Sony Studios in Culver City
- 3:30 p.m. PT: They're expected to arrive at LAX for departure
The Associated Press contributed to this story