The Portuguese had not made the best of starts in a competitive group and it took 53 minutes for Nuno Gomes to break the deadlock against the Belgians.

Two goals from Ronaldo sandwiching one by Ricardo Quaresma then ensured a convincing win for coach Luiz Felipe Scolari and his men.

The third-placed Portuguese are three points behind pool leaders Poland and have a game in hand.

Poland were 5-0 winners against lowly Azerbaijan on Saturday.

The hosts raced into a three-goal lead after just 30 minutes as Jacek Bak, Dariusz Dudka and Wojciech Lobodzinski all netted before Jacek Krzynowek and Przemyslaw Kazmierczak sealed the three points after the interval.

The defeat leaves Azerbaijan rooted to the bottom of the group, while Poland moved two points clear of second-placed Finland, who did not play this weekend.

Serbia passed up the chance to move level on 13 points with Poland when they suffered a shock 2-1 loss to previously winless Kazakhstan.

Kairat Ashirbekov made the breakthrough two minutes into the second half, and Nurbol Zhumaskaliyev doubled the advantage just after the hour mark to put the hosts on course for their first win of the qualifying campaign.

Racing Santander striker Nikola Zigic pulled one back for Javier Clemente's visitors midway through the second period to ensure a nervy end, but Kazakhstan held on for a famous victory.

Zigic let his frustrations get the better of him in injury time and was given his marching orders for violent conduct.