Swimmer Michael Phelps seeks to salvage his London Olympics gold medal bid on Tuesday when he goes in the 200m butterfly final.
The 27-year-old American slumped to a shock fourth in the men's 400m individual medley dominated by Ryan Lochte and then had the unusual sensation of having to settle for silver in the 4x100m freestyle relay.
That medal took Phelps' Olympic career total to 17, leaving him just one short of the all-time biggest career haul of 18 won by Soviet gymnast Larisa Latynina.
But gold is the only colour that really counts for Phelps, who won an extraordinary eight in Beijing four years ago.
Victory on Tuesday would also make Phelps the first man to win the same swimming event at three successive Games.
Australia's James Magnussen has a lot to prove as he tries to shrug off a painful relay loss - a defeat which swimming-mad Australia found hard to stomach - when he starts his bid for the 100m freestyle title.
Magnussen, 21, arrived in London as the overwhelming favorite in the blue riband sprint after bursting on to the international stage with a World Championships triumph in Shanghai last year.
But Magnussen failed to produce the goods in the 4x100 freestyle relay won by surprise packages France on Sunday and must now hope for a confidence-restoring performance against a field that includes world record-holder Cesar Cielo.
"I'm aware he's one of my main competitors," Magnussen said of the big Brazilian. "My biggest competitor is myself and my head space."
France's Camille Muffat and US teen sensation Missy Franklin will go head-to-head in the women's 200m freestyle final as they both attempt to win a second gold at the London Games, although Franklin must do so from lane eight.
In the gymnastics, China's hopes of emulating the success of their men's team by retaining the team title appear slim after they were outclassed by the United States in qualifying.
The Americans' top name Jordyn Wieber has added motivation to lead her team to victory after she suffered the shock of failing to reach the all-around final.
US superstars Kobe Bryant, LeBron James and their star-studded ensemble cast are likely to have lost little sleep over facing Tunisia in their second match of the basketball tournament.
After easing past France in their opener, the Americans looked ominously determined to prove that they are superior to the original Dream Team which lit up the 1992 Barcelona Olympics.
US coach Mike Krzyzewski said he was fast making a team out of a collection of big-name individuals.
"The players have been superb and get along great," he said. "They do have big egos because they are good but it doesn't supersede the team ego."
In the more sedate sport of three-day eventing, Queen Elizabeth II's granddaughter Zara Phillips has a chance of picking up a medal with the British team who go into the final day lying behind defending champions Germany.
While the action will fill the day, the organisers are simply hoping to fill the empty seats at the venues which continued to pop up at the gymnastics and tennis events on Monday.
Under pressure to make progress on the issue -- even Prime Minister David Cameron has called for action -- local organisers LOCOG have put pressure on international sports federations to give up seats they do not need.