There were 12 changes from the Welsh side that beat Fiji a week ago and it showed against Portugal, who are appearing in the tournament for just the second time in their history.
Wales coach Warren Gatland described the fixture as “a slippery one” and so it proved as the underdogs took the game to their more vaunted opponents, who secured a 28-8 victory but will need a vast improvement when they face Australia next weekend.
Despite that Wales have now won 12 of their last 13 pool matches at the World Cup and scored tries through wing Louis Rees-Zammit, hooker Dewi Lake and flanker Jac Morgan, before Taulupe Faletau barged over to secure the bonus point in the final seconds.
Portugal, back at the World Cup for the first time since 2007, played with pace and purpose, especially in the first half, running the ball at every opportunity in an eye-catching display.
They trailed 14-3 at the break but claimed a second-half try via flanker Nicolas Martins after a brilliant line-out move that typified their effort. Portugal did though finish the match with 14 men, after Vincent Pinto’s yellow card was upgraded to a red following a high boot on Josh Adams.
Additional reporting by Reuters.