* Italian scores twice in 4-1 victory
* PSG turn on style in second period (Adds quotes)
ATHENS, Sept 17 (Reuters) - Italian midfielder Thiago Motta scored twice as Paris St Germain romped to a 4-1 win over Olympiakos Piraeus in their Champions League Group C opener on Tuesday.
Edinson Cavani gave Laurent Blanc's side the lead against the run of play with a simple tap-in before Olympiakos levelled when Slovakia forward Vladimir Weiss jinked his way through the defence to score after 25 minutes.
PSG turned on the style in the second half with Motta twice heading in corners from Ezequiel Lavezzi and the Italian turned provider to set up a headed 86th minute goal for debutant Marquinhos.
The Paris club also missed a penalty when Zlatan Ibrahimovic's effort was saved by keeper Roberto in the 82nd minute.
"I was never afraid we might lose," Blanc told reporters. "Olympiakos caused us many problems in the first half.
"They came at us but we knew if we stuck to our game we would get our chances in the second half because they would begin to tire ... and so it proved."
Olympiakos started the game brightly and were unfortunate not to score when Weiss crashed a long-range drive against the bar before rattling the post with another snap shot.
PSG strikers Ibrahimovic and Cavani saw little of the ball in the opening half but the danger they posed was demonstrated in the 19th minute when the Uruguayan tapped in a pass from defender Maxwell.
Olympiakos hit back with a stunning goal as Weiss broke away down the right and skipped past four challenges - including a sublime nutmeg on the 19-year-old Marquinhos - before smashing the ball past keeper Salvatore Sirigu.
Lavezzi came on for Lucas at halftime as Blanc adjusted his attacking options and Cavani and Gregory van der Wiel both tested the reflexes of Roberto with long-range drives.
PSG made it 2-1 when Lavezzi's corner was met perfectly by the unmarked Motta who scored with a stooping header after 68 minutes.
The Italian then escaped the attentions of Olympiakos midfielder Andreas Samaris for a second time to nod his second goal five minutes later.
Ibrahimovic squandered the chance to make it 4-1 when his penalty was saved after the Swede was fouled by Samaris but Marquinhos made amends four minutes later.
"All the intensity, attention to detail, enthusiasm and concentration we had in the first half completely disappeared in the second and that cost us against the quality of opponents we faced," said Olympiakos coach Michel.
"Some things are inexplicable. We could not at any moment of the first half imagine the game would end up this way," the Spaniard added. (Writing by Graham Wood; editing by Tony Jimenez)