Romelu Lukaku claims Belgium have a mentality problem as they fell to a 3-1 defeat against Ukraine in the first leg of their Nations League promotion-relegation play-off.

Lukaku gave Belgium the lead five minutes before the break, rising high to guide Kevin De Bruyne's free-kick into the back of the net for his 86th international goal.

Ukraine rallied after the break and the freshly returned Thibaut Courtois could not keep them out, though they rode their luck, as Oleksandr Zinchenko struck the woodwork with a free-kick with the score still 1-0.

Oleksii Hutsuliak made an instant impact off the bench, slotting home from close range in the 66th minute before two goals in the space of five minutes ensured Ukraine would take a strong advantage into the second leg in Genk.

Vladyslav Vanat put Ukraine ahead, with Illia Zabarnyi helping Zinchenko's looping cross into the back of the net shortly after to ensure Rudi Garcia's first match in charge finished in defeat.

"It was about winning the duels, and we had problems putting pressure," Lukaku said. "That was abundantly clear.

"Especially in midfield, there was not enough pressure. We didn't find any solutions and that's a shame. But after that, it's just about honour.

"It's a matter of mentality. We have a mental problem. I compare it to the previous generation.

"We have to cultivate a mentality as a team again because then we won't concede any goals. That's where it starts, winning duels."

Overall, Belgium contested 72 duels against Ukraine, winning 54.2% of them, while they also won 61.1% of their aerial duels.

However, of the 28 duels in the second half, Belgium won just 39.3% and only came out on top in half of the tackles they put in (3/6).

"Technically, there is a lot of work to be done, but we have to rebuild from scratch," Lukaku added.

"We have a new generation, but we can't lose like this. This is unacceptable. The older players can help with this, but we have to analyse this first.

"Where did it go wrong? In the first half, we found a solution and then it became sloppy. We were afraid on the ball. It is difficult…

"We have to play a kind of total football to win. That starts with making agreements, but now everything was still far too unclear. It was not easy for anyone."