Eintracht Frankfurt fans generate a red-hot atmosphere at Deutsche Bank Park before Tuesday's loss to Napoli.

FRANKFURT, Germany — Napoli coach Luciano Spalletti warned his side's "biggest enemy is to think it's done" after Tuesday's 2-0 last-16, first-leg win against 10-man Eintracht Frankfurt.

Napoli won its first ever Champions League away knockout match thanks to goals either side of halftime from Victor Osimhen and Giovanni Di Lorenzo.

"I am happy with the performance," Spalletti said. "From the start the team played with character, took control of the game and did what we wanted to do.

"We probably had the chance to score an extra goal that could have been useful for us. I still think it is 50-50 for qualification, because there is still a game to be played.

"It was an end-to-end game, which we want and thrive in. We need to stay calm, very calm," Spalletti told Sky Sports of the March 15 return fixture. "There's the second leg still. Our biggest enemy is to think it's done."

Napoli is 15 points clear atop the Serie A table and looks set for its first title in more than 30 years.

Mexico forward Hirving Lozano, who was named player of the match by UEFA, told Sky Sports: "We need to keep working hard to carry on like this. We have to think game by game.

"We did very well against a strong side. It was tough at first but we had a great game."

Frankfurt, who is playing in its debut Champions League season, was reduced to 10 men after 58 minutes when France forward Randal Kolo Muani stepped on the shin of Napoli midfielder Frank Anguissa.

Frankfurt midfielder Mario Goetze said the side was left with an uphill battle after Kolo Muani got his marching orders.

"With the red card, I didn't see it but naturally it was a killer at 1-0 down to go a man down."

After the game, Frankfurt manager Oliver Glasner lamented the "little mistakes we made that Napoli used" to take a lead into the second leg.

"We made a mistake on the halfway line and Napoli had the speed and the quality to use it," Glasner said.

"Then we showed our inexperience and our nervousness — and after the red card, the 2-0 result is to be expected.

"If you've only lost two games in the past eight months, you get a lot of self-confidence and you know what you're doing."

Goetze, who picked up a yellow for complaining to the referee, said he felt the red-card decision was "harsh" against star striker Kolo Muani.

The 2014 World Cup winner added his side needed to be calmer and criticized himself for the error which led to Napoli's opener.

"That cannot happen against a team like Napoli, who can play so well on the counter."

Goetze said he still believed his side could pull off a remarkable comeback.

"They scored two goals here at our home, why can't we do that there? Everything is possible away from home and we'll do everything so that we can make it."