By William Schomberg
RIO DE JANEIRO, June 15 (Reuters) - Argentina must improve on Sunday's unconvincing 2-1 win over World Cup debutants Bosnia if they are to make a serious mark on the tournament, coach Alejandro Sabella said.
The twice world champions struggled to live up to their billing as one of the favourites, especially in the first half of their opening Group F match when they looked unadventurous with five defenders on the field.
They were helped by an early own goal from Sead Kolasinac before Lionel Messi lit up the game in the second half with a signature goal in front of thousands of Argentina fans in the Maracana stadium in Rio de Janeiro.
Sabella said he took heart from Argentina's more creative play once he scrapped his ultra-cautious starting selection at halftime and brought on striker Gonzalo Higuain and midfielder Fernando Gago to give the team more firepower.
"Obviously we need to improve and some of that improvement falls to me," he told reporters, saying he rated Argentina's performance as a six-out-of-10.
"In the first half, I think we controlled the Bosnians well but beyond that we didn't create the kind of depth that we managed in second half."
Sabella told his players at halftime to pass more to Messi and to give him more options when he was on the ball. The advice paid off in the 65th minute when Messi exchanged passes with Higuain and unleashed a crisp shot that went in off the post.
"I think Messi is the best player in world, regardless of what happens in this World Cup, and he's among the best ever players in the history of football, regardless of what happens at this World Cup too," Sabella said.
The diminutive striker agreed that Argentina's performance was not good enough and voiced his frustration at not getting enough of the ball.
"In the first half, it was difficult, because we were playing deep and we let them play," Messi told reporters. "I was alone and it was very difficult.
"We need to improve but the best thing is the result. It is not easy to play the first match at the World Cup with all the nerves and the pressure," he said. (Editing by Ed Osmond)