By Angus MacSwan
PORTO ALEGRE, Brazil, June 25 (Reuters) - Lionel Messi has scored in all of Argentina's group games and while the South Americans clearly depend on the livewire forward, coach Alejandro Sabella is wary of pushing him too hard ahead of the knockout round.
The forward scored twice on Wednesday to help Argentina secure a 3-2 win over African champions Nigeria and clinch first place in Group F for the South Americans.
But Sabella replaced him with Ricardo Alvarez in the 63rd minute, later telling reporters: "We needed Messi to rest."
The 27-year-old, who celebrated his birthday on Tuesday, also got the winner in the 2-1 defeat of Bosnia and the 1-0 victory over Iran as Argentina, one of the pre-tournament favourites, eased towards the last 16.
"We're doing OK," Messi told reporters when asked if he felt tired. "Now we have five or six rest days and I'm doing fine."
After lifting the trophy in 1978 and again in 1986, Sabella said it was about time Argentina won another title.
Messi could not agree more.
"I believe there is nothing more beautiful than being a world champion with the national team, seeing the joy of the whole country," he said.
Sabella was pleased with the way his Argentina side, who will face the runners-up in Group E on Tuesday, played against Nigeria at the Beira Rio stadium in southern Brazil.
"In general the team improved," he said, "they had good control over the ball and were able to damage the opponent."
The coach especially praised the attack, which he said was being refined. Weaknesses, he said, were discussed in private.
But he conceded Argentina had to tighten up defensively.
"We are an offensive team," he told reporters, "and as an offensive team, we sometimes have problems. But our defence is doing a good job and we will try to make it more robust." (Reporting by Angus MacSwan; Written by Esteban Israel; Editing by Ken Ferris)