Second-half goals by David Beckham and substitute Andy Cole gave Manchester United a deserved 2-0 win over Olympiakos Piraeus, the Greek side's first home defeat in 14 Champions League games.
After a close first half, United turned on the style in the second, with Juan Veron again at the heart of most of their fast-paced passing moves as they sought only their second win in 11 away games in Europe.
The opening goal came in the 66th minute when Ryan Giggs did well to cross from the left and Beckham, who scored the last minute equaliser against Greece on Saturday that took England to the World Cup finals, arrived at the far post to touch the ball over the line.
The goal sparked a United purple patch as Giggs went close and Ruud van Nistelrooy hit a post before Cole grabbed the second eight minutes from time, soon after coming on.
In Celtic's match, a strike by Alan Thompson gave Celtic a hard-fought 1-0 victory over Rosenborg Trondheim in theirgroup E clash in the Champions League. Thompson drilled a low free-kick through the Rosenborg wall in the 21st minute, but his side had to withstand a barrage from the Norwegians in the second half.
Celtic's Sweden striker Henrik Larsson, who had scored the winner in last month's 1-0 victory over Porto, missed a chance to make it 2-0 from close range.
The win gave Celtic six points with their second consecutive win, after opening their Champions League campaign with a 3-2 defeat to Juventus in Turin.