Hamburg  - There is all to play for in the Champions League after Tuesday night's first-round matches in the round of the last 16 failed to produce any clear winners.

Inter Milan were held to a goalless draw by Manchester United in Italy, Barcelona played to a 1-1 draw at Olympique Lyon, and former winners Porto drew 2-2 in Madrid against Atletico.

The only victory on the night belonged to Arsenal, who missed a number of excellent chances against AS Roma but still registered a 1- 0 victory through Robin van Persie's first-half penalty.

In Lyon, the home side started like a house on fire with Brazilian midfielder Juninho, who is widely considered the best dead-ball specialist in the world, curling a free-kick over Barcelona goalkeeper Victor Valdes for the opening goal in the seventh minute.

Just two minutes later, French international Karim Benzema should have doubled his side's lead after being sent through, but he pulled his ball just wide.

Barcelona then came back into the game, and top scorer Samuel Eto'o was unlucky not to equalize for the visitors as his 15th-minute strike crashed against the upright and bounced back into play.

In the second half, Barcelona pressed to level matters, and their efforts paid off in the 65th minute when Thierry Henry stole his way past his marker and headed home from close range.

"They played their counterattacks very well, and it was only in the second half that we managed to stop them from doing that," Eto'o said.

Barcelona coach Pep Guardiola said that the 1-1 draw was a first step toward the next round: "We achieved one of our goals, and that was to score in Lyon. Now it is up to us to make sure that we go through at home."

Dutch striker van Persie proved to be Arsenal's match-winner as he earned the Gunners a 36th-minute penalty after being brought down by French defender Philippe Mexes. Van Persie himself took the spot-kick and easily beat Doni.

Arsenal were so eager to get the second half underway that they started the second 45 minutes with just nine men on the field, which resulted in a yellow card for captain Kolo Toure, who ran onto the field without the referee's permission.

The Londoners then had several other good opportunities, but Danish striker Nicklas Bendtner and Emmanuel Eboue failed to make the most of good chances.

The result saw Arsenal stretch their unbeaten home run in the Champions League to 23 matches.

In Milan, the much-anticipated match between Jose Mourinho's Inter Milan and Sir Alex Ferguson's Manchester United failed to live up to its billing, as the defending champions remained unbeaten in the Champions League for 20 games.

The Serie A side surprisingly played a defensive game in the first half and allowed United most of the possession, but they, in turn, failed to make the most of their chances, with Ronaldo and Ryan Giggs coming close but failing to beat Inter goalkeeper Julio Cesar.

World Footballer Ronaldo, who is still waiting for his first Champions League goal of the season, nearly gave United a last-gasp win, with his free-kick in the last minute giving Julio Cesar some problems as the Brazilian failed to hold onto the ball.

Inter captain Javier Zanetti remained optimistic after the game.

"We did not concede a goal. That is good. Now we have to score in Manchester, and even though it will not be easy, it is possible," he said.

"There was very little space out there in the match, and this made it difficult for us to create chances. I am hoping that we can go through."

Argentine striker Lisandro Lopez scored twice in Madrid for former Champions League winners Porto to give his side the advantage ahead of the return leg, after a 2-2 draw against Atletico Madrid.

Maxi Rodriguez opened the scoring for the home side in the third minute after being set up by Diego Maradona's son-in-law Sergio Aguero.

Lisandro equalized for Porto midway through the first half, but Porto's goalkeeper Helton gave the home side another goal two minutes into first-half injury time as he let a speculative Diego Forlan shot slip through his hands.

Lisandro managed to get his sixth Champions League goal of the season in the 72nd minute, when he latched onto a pass from French defender Aly Cissokho to give Porto a deserved share of the spoils.

The return legs are to be played March 10-11. (dpa)