RIO DE JANEIRO, April 22 (Reuters) - Champions Boca Juniors beat UA Maracaibo 3-0 on Tuesday to scrape into the last 16 of the Libertadores Cup on goal difference after Atlas had helped the Argentine side by drawing 1-1 at Colo Colo. Boca pipped Chilean champions Colo Colo on goal difference for second place in Group Three after both finished with 10 points from six games. Mexico's Atlas topped the group with 11 points. If Colo Colo had won, Boca's three-goal win would have been insufficient as they would have finished level on points with Atlas with an inferior goal difference. Boca began needing a five-goal win to qualify without depending on the other game and that appeared on the cards when they raced to a 2-0 lead in 20 minutes against the startled Venezuelans. Defender Gabriel Paletta, who limped off with a thigh injury shortly afterwards, headed the first in the 10th minute from Juan Roman Riquelme's freekick at the Bombonera in Buenos Aires. Ten minutes later, Jesus Datolo scored an individual goal for the Argentines. Boca then squandered a flurry of chances and their frustration mounted with the news that Colo Colo were leading in Santiago. Just as Boca appeared to be losing their way, Atlas equalised to prompt wild celebrations among the Boca fans. Six-times former champions Boca still needed a third goal to go ahead of Colo Colo on goal difference and it finally came in the 74th minute. Martin Palermo flicked the ball to Riquelme and the mercurial playmaker controlled the ball, feigned and then chipped cleverly over goalkeeper Juan Carlos Henao. In Santiago, Colo Colo got off to a flying start when Ricardo Rojas scored from close range in the sixth minute after Domingo Salcedo broke down the left and sent over a low cross. The Chileans failed to build on their early striker and were rocked in the 66th minute when Diego Colotto rose at the far post to head the equaliser following a corner.