Ronaldo teased and tormented the dazed Czech Republic to distraction before his second-half header sent Portugal into the last four with a deserved 1-0 win over limited opponents.
The world's most expensive player met Joao Moutinho's cross after 79 minutes to secure Portugal, who are in the semi-finals of a European Championship for the third time in the last four tournaments, a clash with holders Spain or France on Wednesday.
"I think we have showed quality and consistency," said Portugal coach Paulo Bento. "We had the capacity to react. We switched well from defence to ttack."
With Ronaldo again in irrepressible form after running the Netherlands ragged and scoring twice in their final group stage game, Portugal look set for a bold bid to emulate their run to the 2004 final on home soil, before Greece spoiled the Portuguese party with a shock victory.
"It doesn't matter who will be our opponents, be it France or Spain," Bento added. "We will do the best to reach our goal."
It was surprising it took Bento's side so long to break down the Czechs, who badly missed injured playmaker Tomas Rosicky and failed to trouble Portugal keeper Rui Patricio throughout.
Ronaldo had twice hit the woodwork, once from a sublime moment of skill late in the first half and again from a long-range free-kick just after the break, but he was not denied a third time when the impressive Moutinho swung over a cross from the right and the forward headed firmly down and past Petr Cech.
The showman, winning his 94th cap for Portugal, celebrated his thrd goal of the tournament by beating his chest, then blowing kisses into a television camera as his team mates, playing their role of support cast to aplomb, mobbed him.
"We had a lot of opportunities. The Czechs did not have any - that's a great game," the Portugal captain told reporters.
"I think the chances [of reaching the final] are 50/50 and we just have to believe in it."
With 35 goals for his country, the 27-year-old will no doubt go on to surpass Eusebio (41), and then Pauleta (47) as Portugal's top scorer. The debate over whether he, or Argentine Lionel Messi, is the best of a generation will rage on.
The only blot on Portugal's victory came late in the first half when striker Helder Postiga went down clutching his right hamstring and had to be carried off the pitch on a stretcher.
The hard-working centre-forward must now be a major doubt for the semi-final in Donetsk.
After frustrating Portugal in a cagey and disjointed first half, the Czechs ran out of puff as Cech bailed out his tiring defence with some smart saves before the inevitable goal came.
The match statistics indicated a barrage against shot-shy opponents by Portugal who had 20 shots with five on target.
The Czechs reached the knockout stage as group winners, despite a negative goal difference bu
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