Ronaldo secured Real Madrid's Champions League quarter-final passage with a first-half strike that gave the champions a 1-0 win at Lokomotiv Moscow this evening.
The victory eliminated Borussia Dortmund, who secured a 1-0 win over AC Milan at the San Siro in the other group match although their valiant effort was all for nothing.
Milan topped the group table on 12 points, one point ahead of Real. The German champions finished with 10 points, while Lokomotiv finished bottom with just a single point after holding Real to a 2-2 draw in Madrid last December.
Ronaldo, voted World Player of the Year in 2002 for the third time in his career, headed home from close range in the 35th minute after a pinpoint cross by Luis Figo.
The Russian champions pressed for an equaliser in the final minutes, but rarely threatened a formidable Real defence.
It was a mostly uneventful match, played on a dreadful pitch covered with sand, not dissimilar to Chelsea's Stamford Bridge surface earlier this season.
It was Madrid's first victory in Moscow after eight previous visits to the Russian capital had ended in draws or defeats.
Meanwhile, Dortmund were edged out despite winning 1-0 at the Group C winners.
The victory, secured by Jan Koller's 80th minute goal, would have been enough for the Germans to join Milan had Madrid not won themselves.
Dortmund's exit from the competition means Germany is without a representative in the last eight for the first time in 19 years.
Milan, five-time European champions, came close to breaking the deadlock in the fourth minute at the San Siro.
Portugese playmaker Rui Costa threaded a beautifully-weighted pass to Rivaldo, who was denied by a fingertip save form Borussia goalkeeper Jens Lehmann.
Evanilson was the first to threaten for the visitors, but the Brazilian's long range effort sailed high over the bar. A dull first-half ended with Alessandro Nesta's perfectly-timed sliding tackle denying Borussia's Brazilian striker Amoroso a shot on goal as the Brazilian burst into the penalty box.
Rui Costa was at the heart of every Milan move and he almost provided team-mate Rene Gattuso with the opening goal in the 58th minute, but the former Rangers midfielder saw his powerful shot strike the post.
Four minutes later Dortmund were denied when Amoroso's 25-yard curling shot was brilliantly clawed away by Milan goalkeeper Christian Abbiati.
Dortmund's pressure eventually told with 10 minutes to go when Koller broke Milan's offside trap to latch onto Lars Ricken's angled pass and drill a low shot beyond Abbiati.
Milan had strong appeals for a penalty waved away moments later when Fillipo Inzaghi fell in the penalty area under Christian Worms' challenge.
But the linesman's flag was already raised as Inzaghi had strayed into an offside position before the tackle came in from the German defender.