Great Britain's veteran Welsh captain Ryan Giggs and Swansea City's Scott Sinclair scored as they beat the United Arab Emirates 3-1 at Wembley.
A win or draw against Uruguay at the Millennium Stadium on Wednesday will see them through to the quarter-finals.
Earlier Nicole Cooke relinquished her women's road race Olympic title, crushing hopes of being Wales' first medallist at the London Games.
And Sarah Thomas scored in GB women's hockey's 4-0 Group A win over Japan.
Four years ago in Beijing, 29-year-old cyclist Cooke sparked Great Britain's gold rush in typically tenacious fashion, but finished 31st at the Mall.
But she was unable to repeat the feat as Dutch rider Marianne Vos won gold and GB's Lizzie Armitstead took silver.
Welterweight Fred Evans advanced to the last 16 in the boxing with an 18-10 points victory over Algeria's Ilyas Abbadi and will next face Egidijus Kavaliauskas of Lithuania on Friday.
In the pool, Georgia Davies' first appearance in an Olympic 100m backstroke competition ended in the semi-finals, where the 21-year-old finished eighth in 1 minute 00.5 seconds, having qualified from the heats earlier in the day in 59.92 secs.
Ieuan Lloyd also missed out on a place in the 200m freestyle semi-final after finishing sixth in his heat and 19th overall.
There was disappointment too for Welsh women's skeet shooter Elena Allen.
The Russian-born 40-year-old finished 14th with a score of 60 in the heats, failing to qualify for the final at the Royal Artillery Barracks in Woolwich.
At the rowing at Eton Dorney, Victoria Thornley and the women's eight will compete in Tuesday's repechage after finishing third in their heat.