Portugal's first spell of pressure started on 13 minutes when the lively Joao Moutinho put Joao Pereira through with a fine pass but the right-back's shot was blocked by keeper Antonis Georgallidis.
Just as Portugal's menace was starting to wane, Cyprus midfielder Sinisa Dobrasinovic stretched out his arm inside the box to deflect a Moutinho shot, received a second booking and allowed Ronaldo to slot in coolly from the resulting penalty on 35 minutes.
Portugal took advantage of the added space in midfield, with both Moutinho and striker Helder Postiga coming close to doubling their lead with fierce, long-distance efforts just before the break.
"We played well in the first half, especially until we scored. The score could have been bigger in the first 45 minutes," Portuguese coach Paulo Bento said.
The Cypriots returned with an even more defensive attitude and Portugal's passing game stalled. They threatened only with a fierce shot by Ronaldo on 51 minutes, which the keeper blocked, and a diagonal drive from Fabio Coentrao that hit the post six minutes later.
"After we were reduced to 10 men it was very hard for us, we had to chase Portugal, ran out of stamina and that's why we collapsed at the end," Cyprus coach Nikos Nioplias said.
The Portuguese left it late to secure the win, with captain Ronaldo sidestepping a defender near the box to create space and fire in his second goal in the 82nd minute. Two minutes later the forward used his speed on the left wing and set up substitute Almeida for a simple tap-in.
Winger Danny came on to complete the rout by cutting in from the left and driving in the fourth goal in injury-time.
"The goals at the end brought justice. There were times when we did not play well in the second half, but the most important thing was to improve our goal difference," Bento said. "We go into the last two qualifying matches in a strong position."
Portugal are level on 13 points with Norway, who beat Iceland 1-0 at home. The Portuguese play Iceland at home and Denmark away in October.
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