Matsumoto wins Japan's first gold medal of the Games in the women's judo 57kg category, while India's shooting champion fails to repeat his 2008 gold.
Olympics: Round-up of action from Day 3 at London 2012
Ihab Almatbouli made history as he became the first boxer from Jordan to win an Olympic bout.
The 26 year old put on a classy display to defeat Nigerian Lukmon Lawal 19-7 in a light-heavyweight contest.
Alamtbouli, who lives in and comes from the Palestinian refugee camp of Al-Baqaa (which has a population of around a 100,000) on the outskirts of Amman, was already the first Jordanian to qualify for the Games.
Now he hopes his latest effort will cement his role model status
"I hope due to all my achievements I am going to be a role model especially to the young back home," said Almatbouli, who relaxed in the third round and indulged in some crowd pleasing showboating.
"It will mean a lot back home in Baqaa to everybody as we are a tight knit community and everyone knows each other. My brothers (he is the second oldest of six) are all boxers and will have been watching like most other people there."
Kaori Matsumoto won Japan's first judo gold in London in the women's -57kg category, while French president Francois Hollande watched in delight as France picked up their second women's judo medal of the Games.
Matsumoto, 24, the world No 1, who had been fast, aggressive and determined throughout the tournament, won the final after Corina Caprioriu of Romania was penalised for a leg grab.
Japan traditionally dominates judo at the Olympics but this was the first medal won by one of the team's women.
Earlier, she had beaten Italian Giulia Quintavalle, the reigning champion, in the quarter-final before overcoming France's Automne Pavia in the semis.
Caprioriu, the 26-year-old sixth seed, reached the final by beating American Marti Malloy in the last four with an automatic winning ippon, throwing her to the tatami (mat) with just seconds left.
Russia's Mansur Isaev won the men's 73kg category, taking the second gold medal for his country in judo in a matter of days.
Fourth seed Isaev, 25, came out on top in a fast and furious fight with Japan's Riki Nakaya.
He deserved gold after beating Nakaya, the world No 2, and reaching the final by overcoming South Korea's Wang Ki-Chun, the world No 1 and silver medal winner in Beijing.
He emulated the success of countryman Arsen Galstyan on Saturday who had won Russia's first judo gold since the collapse of the Soviet Union.
Mongolia's Nyam-Ochir Sainjargal took bronze by beating Dutchman Dex Elmont whose brother Guillaume will compete in the -81 kg section on Tuesday.
It means Mongolia have now won judo medals at every games since Athens in 2004.
France's Ugo Legrand defeated Wang to win the other bronze, his country's third judo bronze medal in London, and received a standing ovation from watching French President Francois Hollande, who greeted him enthusiastically after his win.
Alin George Moldoveanu of Romania won the Olympic gold medal in 10-metre air rifle after equaling the Olympic qualifying record.
The victory made up for missing a medal in the same event in the Beijing Games by 2 millimetres.
Moldoveanu and top-ranked Niccolo Campriani of Italy shot 599 in qualifying to tie the Olympic record by Zhu Qinan in 2004.
In the 10-shot final, Moldoveanu was just a little more consistent, scoring 103.1 to Campriani's 102.5 for the silver.
Gagan Narang of India won the bronze.
Indian Olympic champion Abhinav Bindra failed to repeat his feat in Beijing, where he became his country's first individual gold medallist.
Bindra, 29, was in contention to reach the final at the Royal Artillery Barracks but slipped down the rankings to finish 16th in qualifying. Only the top eight went through to the final.
The Indian, who has slipped to number 20 in the world, fell away towards the end of the session, admitting: "It didn't go well in my last 10 shots."
"It was hard at the end because it was closing in," he added. "There was a lot of noise. It was difficult to keep the momentum going but today I just did not have it in me to keep that going to the last."
"I'm looking forward to going home. I've been away for six weeks," he said. "I'm looking forward to being with my family for a while."
When asked about whether he was eyeing the 2016 Games in Rio de Janeiro, he said: "Perhaps, why not? I don't know."
Andy Roddick found his form quickly in his first Olympic match, beating Martin Klizan of Slovakia, 7-5, 6-4 in the first round at Wimbledon.
Roddick converted only two of 13 break-point chances but dominated with his serve, as often happens at Wimbledon, where he's a two-time runner-up.
"I served really well," he said. "I would have liked to have converted more break points. But I got a couple and, thankfully, that's all I needed."
The Olympic match, delayed one day by rain, was Roddick's first in eight years. He lost in the third round at the 2004 Games and skipped Beijing in 2008.
As a price for being unseeded, he'll face a daunting challenge in the second round: Novak Djokovic, the 2011 Wimbledon champion.
"The guy has been the best player in the world over the last couple of years," Roddick said. "It's going to be tough. But the situation, we've both been through it a million times. I'm going to have to serve well and take some chances on returns."
Lleyton Hewitt of Australian and Nikolay Davydenko of Russia, both three-time Olympians, won their opening matches. No 9-seeded Juan Monaco of Argentina, No 13 Marin Cilic of Croatia, No 16 Richard Gasquet of France and big-serving Milos Raonic of Canada also advanced.
Cao Yuan and Zhang Yanquan won the men's 10-metre synchronized title, giving China its second diving gold medal of the London Games.
Cao and Zhang totaled 486.78 points in the six-dive final Monday, spoiling the medal hopes of Brits Tom Daley and Peter Waterfield, who were shut out.
German Sanchez and Ivan Garcia of Mexico won the silver with 468.90.
Nick McCrory and David Boudia of the U.S. took the bronze with 463.47.
Daley and Waterfield led through the first three rounds, but botched their fourth dive and dropped to fourth, where they eventually finished.