The reigning Champions League winners began the defence of their crown with a disappointing 0-0 draw against Villarreal at Old Trafford.

Ronaldo's second-half introduction certainly sent a surge through United - and dispelled any doubts the summer transfer saga with Real Madrid would affect his popularity.

But United could come no closer than a late Jonny Evans diving header that bounced back off a post as their 12-game winning streak on home soil in the competition was brought to an end.

The Yellow Submarines almost sank Sir Alex Ferguson's men altogether when Guille Franco hit the woodwork as well.

Elsewhere, Arsenal captain William Gallas bundled in a late equaliser to rescue a point from the Gunners' opening Group G game against Dynamo Kiev in the Ukraine.

Emmanuel Adebayor, Robin van Persie, twice, and Cesc Fabregas all had good first-half chances for the Premier League club, which is still yet to win a European tie in the former Soviet Union.

Kiev looked to have made Arsenal pay a heavy price when, on 64 minutes, Bacary Sagna was adjudged to have pushed over Ognjen Vukojevic and Ismael Bangoura scored from the penalty spot.

Then, just as time looked to be running out, Gallas - who had made a mistake in the build-up to the goal - netted at close range following a low cross by Theo Walcott.

Barry Robson missed a first-half penalty as Celtic drew a blank in its Champions League Group E opener against Aalborg.

The failure to pick up maximum points at Parkhead put an immediate dent in its hopes of reaching the last 16 from a group which also includes Manchester United and Villarreal.

The home side huffed and puffed against the unfancied Danish club and was awarded a spot-kick in the 29th minute when midfielder Shaun Maloney was tripped by Steve Olfers inside the box.

But Robson stepped up to blast his shot at the legs of goalkeeper Karim Zaza and the score remained 0-0 for the following hour.

Lyon scored twice in the final 17 minutes to deny Fiorentina all three points in a pulsating Group F clash at the Stade Gerland.

Italy striker Alberto Gilardino put the visitors two goals ahead by the interval after directing home headers at the start and end of the first half.

But Lyon launched a superb comeback, halving the deficit in controversial circumstances after they refused to kick the ball out of play with Fiorentina defender Luciano Zauri down injured. Frederic Piquionne eventually found the net amid furious Viola appealing.

Karim Benzema then capped the revival by slamming home a deflected shot in the 86th minute.

Bayern Munich enjoyed a winning start in Group F by overcoming a battling Steaua Bucharest side 1-0.

Daniel Van Buyten scored the game's only goal in the first half before the visitors held off a second-half onslaught in the Romanian capital.

Luis Aragones' worries at Fenerbahce grew a little deeper as his side began its Group G campaign with a 3-1 loss at Porto.

Porto led through early goals from Leonardo Lopez and Lucho Gonzalez, and although Daniel Guiza got one back against the run of play, Fener rarely threatened an equaliser before Lino capped the win at the death.

Real Madrid cruised to a 2-0 result over 10-man BATE Borisov on in Group H.

Goals from Sergio Ramos and Ruud van Nistelrooy had Madrid firmly in control before BATE's Anri Khagush was dismissed to make an uphill task all-but impossible.

A second-half goal from Alessandro Del Piero was enough for Juventus to see off the challenge of Zenit St Petersburg in their Champions League Group H opener.

The veteran striker powered home a free-kick to keep the points in Turin.

Champions League
Group E
Celtic 0
Aalborg BK 0

Manchester Uniter 0
Villarreal 0

Group F
Lyon 2
Piquionne 73, Benzema 85
Fiorentina 2
Gilardino 12, 42

Steaua Bucuresti 0
Bayern Munich 1
Buyten 14

Group G
Dynamo Kyiv 1
Bangoura 64p
Arsenal 1
Gallas 88

FC Porto 3
Lopez 11, Gonzelez 14, Lino 90
Fenerbahce 1
Guize 29

Group H
Juventus 1
Piero 76
Zenit St. Petersburg 0

Real Madrid 2
Ramos 11, Van Nistelrooy 57
BATE Borisov 0