Deportivo Coruna ended Monaco's 100 percent start with a 1-0 win, 10-men Anderlecht defeated Celtic 1-0 while Dynamo Kiev's 2-1 victory over Arsenal left the English premier league club struggling to qualify for the knockout stages.
Inter, who sacked Argentine coach Cuper on Sunday and replaced him with former AC Milan boss Alberto Zaccheroni after a poor run in Serie A, had their 100 percent record in this season's competition ended abruptly in the Russian capital.
Assistant coach Corrado Verdelli took temporary charge on Tuesday but Inter were a pale shadow of the side that were so impressive in humiliating Arsenal 3-0 at Highbury in their opening Group B fixture last month.
"We just made too many mistakes as we tried to score, missing a lot of chances, and also we gave up too many balls in midfield," said Verdelli.
"Of course, this defeat is a big blow for us, both mentally and in terms of points. But I'm sure in the next few days when things start returning to normal we'll again be a team contending for all the trophies we are competing in."
Lokomotiv had not scored in their six previous Champions League games but took just two minutes to go ahead on a freezing night in Moscow, skipper Dmitry Loskov converting from close range after two minutes.
Georgia striker Mikheil Ashvetia and Russian international Dmitry Khokhlov, with an imperious header, completed the rout with two goals seven minutes apart shortly after the interval.
WOEFUL DEFENDING
Inter still lead the group but were joined on six points by Dynamo Kiev. The Ukrainian champions were helped by some woeful Arsenal defending as they took a two-goal lead, but then had to survive a late Arsenal onslaught.
A mix-up between Edu and Gilberto Silva allowed Maxim Shatskikh to volley home from 15 metres in the 27th minute.
A mistake from Arsenal goalkeeper Jens Lehmann gifted Valentin Belkevich a second goal just after the hour before Thierry Henry set up a rousing finale 10 minutes from time. Kolo Toure then hit the bar in stoppage time but Kiev held on.
"Now all the players are down and they need to get over it. But the team spirit is good," said Arsenal manager Arsene Wenger. "We now have two home matches and we will try and get the maximum number of points."
Last season's beaten finalists Juve made it three wins from three in Group D as Sociedad, who had also made a perfect start to their first appearance in Europe's premier club competition for 21 seasons, suffered a rude awakening at the Delle Alpi.
Juventus flew into a two-goal lead after just seven minutes. France striker David Trezeguet sprang the offside trap for the first on three minutes, then Marco Di Vaio gathered Pavel Nedved's superb crossfield pass before cutting inside and curling home a shot from 25 metres past Sander Westerveld.
Di Vaio headed a third goal from Gianluca Zambrotta's cross in first-half injury time. Trezeguet made it 4-0 on 63 minutes before an own goal from Igor Tudor and a Francisco de Pedro strike gave the scoreline some respectability.
EVENLY POISED
Brazilian striker Giovane Elber failed to find the net for Olympique Lyon against his former club Bayern Munich, but a goal two minutes from time by Peguy Luyindula rescued a 1-1 draw for the French champions to leave Group A evenly poised.
Dutch striker Roy Makaay, with his third Champions League goal for Bayern in three games since joining from Deportivo Coruna for a club record 18.75 million euros ($21.16 million), had fired the visitors into a 25th minute lead.
Elber was denied a goal right at the death as Oliver Kahn denied him with a superb reflex save.
Bayern lead the group with five points, one more than Lyon and Anderlecht while Celtic have three.
Anderlecht had defender Glen De Boeck sent off in the 26th minute against Celtic but the Belgian side repelled everything the visitors could throw at them.
The winner came on 71 minutes when Ivory Coast striker Aruna Dindane converted after a fine run and cross from Christian Wilhelmsson.
Unbeaten Deportivo Coruna leapfrogged Monaco at the top of Group C, a late goal from striker Diego Tristan handing Deportivo a narrow victory at the Riazor.
PSV Eindhoven picked up their first win and points after an error from AEK Athens keeper Christostomos Michailidis, whose poor throw let in Theo Lucius on 37 minutes. AEK also had Kofi Amponsah sent off after 65 minutes to compound their misery.
Galatasaray's 1-0 win at home to Olympiakos in Group D left the Greek side as the only team so far without a point in the competition. Cihan Haspolatli got the goal after eight minutes.
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