The Portuguese side on Tuesday thumped AS Roma 3-0 in the Italian capital to win 4-1 on aggregate, reports Xinhua.
Roma, who battled to a 1-1 draw in the first leg in Portugal, fell behind in the 8th minute on a goal by Porto's Felipe, while visiting goalkeeper Iker Casillas made a pair of key stops.
The home team was reduced to nine men with the expulsions on either side of half-time of Daniele de Rossi and Emerson Palmieri and conceded two more goals in the final 20 minutes.
AS Monaco, who entered Tuesday's battle with a 2-1 advantage after the first leg in Villarreal, kept the Spanish club bottled up for most of the match.
The visitors' first shot on goal came only in the 40th minute and Monaco made it 1-0 on the night and 3-1 on aggregate when Fabinho converted a penalty in the 91st minute.
Celtic, meanwhile, conceded two goals on the road against Hapoel Beer Sheva, but survived 5-4 overall on the strength of their 5-2 victory in the first leg in Glasgow.
In Warsaw, Irish first division champions Dundalk jumped ahead 1-0 in the 19th minute on Robbie Benson's goal to move within striking distance after losing 2-0 at home in the first leg.
But the side hoping to become Ireland's first-ever Champions League qualifier was unable to press their advantage and Michal Kucharczyk scored for Ligia in the final minute to bring the aggregate score to 3-1 for the Polish club.
Bulgaria's Ludogorets are headed to the Champions group stage for the second time after a 2-2 draw at home against Viktoria Plzen, who lost the first leg 2-0 in the Czech Republic.
