Dries Mertens says Belgium will improve in their second World Cup match despite beating Panama 3-0 on Monday.
The Belgians endured a disappointing first-half before reemerging from the break intent on breaking down their Central American opponents.
Mertens scored an audacious volley just after the restart, before Romelu Lukaku's double rounded off the victory.
And the Napoli striker told reporters after the game that the Red Devils should produce a more well-rounded effort in their next match against Tunisia.
He said: "It was difficult. You start a World Championship with a long build-up and then that race is there, where you have so much sense. But it is exactly as if the legs did not want to join in.
"I think you'll see it with every team in the first race, also at this World Cup. Hopefully the second game will be better."