Dries Mertens started this season where he left off the last, setting Napoli on its way to a 2-0 win over nine-man Nice in the first leg of their Champions League playoff on Wednesday.

Mertens scored more than 30 goals last season for Napoli, with five of them in the Champions League. And it took the Belgium international less than 13 minutes to open his account for this campaign.

Mertens sprung the offside trap to race onto a through-ball, take it past onrushing goalkeeper Yoan Cardinale and slot it into the empty net.

The 30-year-old forward was instrumental in Napoli's second, winning a penalty when he was tripped by Christophe Jallet just inside the area. Jorginho converted the spot-kick in the 70th minute.

"Today was a very important match, we told ourselves that. The team played well and gave everything," Mertens said. "But I think 2-0 is too little. It's not bad, but if we watch the match again I think it's too little looking at our performance."

Nice's night went from bad to worse 12 minutes from time when midfielder Vincent Koziello was shown a straight red card for a challenge on Napoli's Piotr Zielinski and teammate Alassane Plea followed him off the pitch after receiving a second yellow for dissent.

"We could have avoided the two red cards, but it's a bit harsh," Nice coach Lucien Favre said. "It's regrettable to finish with nine men, but what's good is that we kept the scoreline the same because at 3-0 down we would have been done for. While now, there's still hope."

Nice struggled to create anything without injured duo Mario Balotelli and Wesley Sneijder, who both used to play in Italy. The French side will hope to have them back for the second leg on Tuesday.

A look at the other playoff first legs:

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CELTIC 5, ASTANA 0

Celtic will be confident of reaching the group stage for a second successive season after recording the biggest margin of victory for a home side in a Champions League play-off match.

The Scottish side knocked Astana out in the third qualifying round last season 3-2 on aggregate and only a remarkable turnaround in Kazakhstan will prevent a repeat.

Astana defender Evgeni Postnikov turned Tom Rogic's strike into his own net shortly after the half hour and Scott Sinclair doubled Celtic's lead just before halftime.

Sinclair scored his second on the hour and further goals from James Forrest and Leigh Griffiths sealed a comfortable victory.

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ISTANBUL BASAKSEHIR 1, SEVILLA 2

Champions League newcomer Istanbul Basaksehir faces a tough task to reach the group stage after allowing Sevilla two away goals.

Under a torrential downpour, Sergio Escudero opened the scoring for the Spanish side in the 16th minute with a low shot into the bottom far corner.

Eljero Elia levelled shortly after the hour mark, but Wissam Ben Yedder secured the win six minutes from time.

Sevilla reached the round of 16 last season, but lost 3-2 on aggregate to Leicester.

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HAPOEL BEER-SHEVA 2, MARIBOR 1

There was an early scare for Beer-Sheva in its bid for a first appearance in the group stage.

Marcos Tavares took advantage of a defensive error to fire Maribor ahead in the 10th minute, but Anthony Nwakaeme equalized two minutes later with a spectacular volley into the roof of the net.

Shir Tzedek converted a penalty in first-half stoppage time to put the home side ahead after Maor Melikson was fouled by Blaz Vrhovec.

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OLYMPIAKOS 2, RIJEKA 1

Alaixys Romao scored in stoppage time to complete a turnaround for Olympiakos against Rijeka.

Vadis Odjidja-Ofoe had scored an emphatic equalizer in the 66th minute to cancel out Heber's first-half opener for Rijeka.

But the Croatian side went down to 10 men when Leonard Zhuta was shown a second yellow card seven minutes from time.

And Romao hooked in the winner from close range for Olympiakos, which had also hit the bar moments earlier.

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