* Holders Chelsea exit despite big victory
* Juventus end Chelsea interest
* Galatasaray and Celtic into last 16
* Messi suffers knee injury (adds details, quotes)
LONDON, Dec 5 (Reuters) - Less than seven months after celebrating a first Champions League triumph to satisfy owner Roman Abramovich's thirst for continental dominance, Chelsea became European chumps on Wednesday despite a rip-roaring but irrelevant finale.
A 6-1 rout of Nordsjaelland at Stamford Bridge handed beleaguered interim manager Rafael Benitez some respite but it came with the unwanted distinction of becoming the first Champions League holders to exit at the group stage.
Chelsea's victory, their first since the Spaniard replaced the sacked Roberto Di Matteo a fortnight ago, mattered little with Juventus reaching the last 16 thanks to a 1-0 win in Ukraine over Shakhtar Donetsk.
A second-half own goal was enough for the Italians to secure top spot in Group E and progress alongside Shakhtar.
Chelsea, who needed to win and hope Juventus lost, head into the Europa League with the West London aristocrats unlikely to be celebrating Thursday night football that Europe's second-tier competition will bring in the new year.
Galatasaray and Celtic claimed the other two knockout stage places decided in the final round of group matches and there were injury concerns for Barcelona after Argentine World Player of the Year Lionel Messi suffered a bruised knee.
Chelsea finally found their stride following two draws and a defeat under Benitez, but the Spaniard was still subjected to occasional jeers by fans still unhappy at popular Di Matteo's exit.
Fernando Torres scored twice in an entertaining clash that featured three penalties, all awarded for handball and two of which were saved, in six first-half minutes.
David Luiz, Gary Cahill, Juan Mata and Oscar also netted to leave Benitez optimistic that brighter days lie ahead.
"It was important to win but also the way we won and the way we played. We saw character, attitude, commitment and intensity so I'm pleased for them, for the fans, and for me," he told reporters.
"For me tonight was the confirmation of everything I was watching in the training sessions. The main thing with Fernando Torres is that if we create chances, he will score goals."
Juventus ended Shakhtar's unbeaten home run stretching to 16 games in all competitions with Olexandr Kucher, trying to stop Sebastian Giovinco meeting a cross from Stephan Lichtsteiner, putting through his own net for the only goal on 56 minutes.
Celtic struck a blow for Scottish football by reaching the last 16 for the first time since the 2007-08 season thanks to a 2-1 home victory over Spartak Moscow which secured runners-up spot behind Barcelona in Group G.
The final whistle ignited raucous celebrations in the east end of Glasgow and manager Neil Lennon described reaching the knockout stages as a "monumental achievement".
"This campaign has been a great learning process and these young lads have grown as its gone on. This is the premier event, the toughest of the toughest. No-one gave us a prayer going into this group," Lennon, whose side beat Barca at home last month, told Sky Sports.
Kris Commons won it for Celtic with an 81st-minute penalty after Spartak's Ari had cancelled out Gary Hooper's opener.
Benfica, who began the night level on points with Celtic, could not find the breakthrough they needed in a 0-0 draw away against below-strength Barcelona, who will be more worried about Messi's injury.
Messi, a second-half substitute, collapsed to the ground clutching the back of the knee after colliding with Benfica goalkeeper Artur and looked to be in severe discomfort as he was taken from the pitch.
Barca said on their Twitter feed he had suffered bruising on the outside of the knee and would undergo further tests to determine the extent of the damage.
Second-half goals from Burak Yilmaz and Aydin Yilmaz helped Galatasaray come from behind to win 2-1 at Braga and go through as Group H runners-up behind Premier League leaders Manchester United.
The Turkish side denied Romania's CFR Cluj, whose consolation for an upset 1-0 victory over former champions United at Old Trafford, was a Europa League place.
Brazilian Luis Alberto's fine 55th-minute strike won it for Cluj against a United side featuring wholesale changes.
Last season's beaten finalists Bayern Munich finished top of Group F after a 4-1 rout of BATE Borisov, ending level on points with Valencia but with a better head-to-head record against the Spaniards who beat Lille 1-0 in France
Swiss international Xherdan Shaqiri scored one and set up another for Bayern, who exacted revenge for a shock defeat in the reverse fixture in Belarus.
Both sides finished with 10 men, Bayern having Jerome Boateng dismissed early in the second half while Denis Polyakov was ordered off for BATE.
The draw for the last 16 takes place on Dec. 20. (Editing by Ed Osmond)