Champions League title holders Porto face a struggle to qualify for the knockout phase after Paris St Germain held them to an uninspired 0-0 draw on Tuesday.
The 2004 winners remain rooted to the bottom of Group H with two points from four games after a scrappy, rain-soaked match where they enjoyed most of the possession but failed to capitalise on their chances.
Brazilians Derlei and Diego and Portugal midfielder Maniche all squandered opportunities while PSG, apart from some spirited moments in the last 10 minutes, looked happy with a draw.
With Chelsea already qualified from the group with a maximum 12 points from four games, Porto and PSG must fight it out with CSKA Moscow, on four points alongside the French side, for the second qualifying spot.
Poor passing and finishing let down Victor Fernandez's Porto, who have struggled with their form after losing coach Jose Mourinho to Chelsea at the end of last season.
Maniche put a volley wide in the 19th minute and broke though at the end of the half but he shot high under pressure.
Diego produced the only shot on target in the first half but he scuffed the ball straight at PSG goalkeeper Lionel Letizi.
Brazilian playmaker Derlei then missed a sitter from a pinpoint Maniche cross in first-half injury time, heading wide with the goal at his mercy.
Benni McCarthy also put a diving header wide early in the second half.
NO BLAME
"The team really worked hard for victory from the start and did everything they could. I cannot blame them," Fernandez said. "The only thing missing was getting the ball once in the net."
PSG relied on the counter-attack but Porto proved expert at catching Pauleta offside.
Only in the dying minutes did the French side look really dangerous, substitute Bernard Mendy forcing Vitor Baia to close him down for a fine save.
Vitor Baia then tipped the ball over from the resulting curling Mendy corner.
Letizi ensured PSG returned with a point by keeping out a last ditch effort from Ricardo Costa in injury time.
"We came here to avoid losing and we played a good game because we were well organised," PSG coach Vahid Halilhodzic said. "It's the first time we haven't conceded outside Paris which shows we are getting better. We defended well and we also had chances.
"I'm disappointed in the European champions...I think the best opportunities to score were ours."
Fernandez said Porto's future in the competition now lay in the balance.
"Our future now does not depend only on us but on the results of others. It is now essential to win in Moscow and then wait and see what happens in the last game," he said.
Porto face Chelsea at home in the last match of the first round.
