* Forward grabs brace in 4-1 victory over Cameroon
* Fred also scores as Brazil claim top spot in Group A
* Brazil to play South American rivals Chile in last 16 (Writes through, adds quotes, details)
By Iain Rogers
BRASILIA, June 23 (Reuters) - Brazil forward Neymar shot to the top of the World Cup scoring charts with a superb double in a convincing 4-1 win for the hosts over Cameroon on Monday that sent them through as Group A winners to face Chile in the last 16.
After grabbing a brace in Brazil's 3-1 win over Croatia in their opening game, Neymar was again the star of the show at an electric national stadium and with four goals leads a chasing pack on three including Germany's Thomas Mueller and Karim Benzema of France.
Neymar struck twice in the first half either side of Joel Matip's effort for the already-eliminated Africans, Fred nodded home at the start of the second and substitute Fernandinho added a late fourth.
The sparkling performance, with poster-boy Neymar wowing the crowd with his trademark flicks and feints, meant Brazil went some way to dispelling doubts about their title credentials following last week's drab goalless draw with Mexico.
Their title rivals will have noted with interest, however, that Cameroon caused problems for the Brazilian defenders and with more accomplished forwards, such as injured captain Samuel Eto'o who was on the bench, might have pulled off an upset.
"I like the way the team played," Brazil coach Luiz Felipe Scolari told a news conference.
"There were some highs and lows which is normal and sometimes we lost the ball in midfield which made us anxious," he added.
"Even though we had difficulties, we could have scored seven or eight and conceded a couple more goals.
"We have improved again and for the next game we should improve a little bit more."
Mexico finished level on seven points with Brazil thanks to their 3-1 victory over Croatia and went through in second place due to an inferior goal difference. They will play Group A winners the Netherlands, who beat Chile 2-0 on Monday.
Mexico took a 3-0 lead with late goals in Recife, rattling Brazilian nerves until Fernandinho, who was introduced at halftime, made it 4-1 and Croatia pulled one back.
The fired-up Brazilian players made a blistering start at the vast arena in the capital, where the stands had been transformed into a sea of yellow by expectant home fans.
Hulk, back in the side after recovering from a muscle strain, was causing early problems down the right but Cameroon gradually played their way into the game before Neymar struck his first of the night after 17 minutes.
Luiz Gustavo won the ball on the left and his low cross was perfectly weighted for the 22-year-old, in space in the centre of the penalty area, to deftly guide the ball into the corner.
It was the 100th goal of this World Cup finals on Brazil's 100th appearance in soccer's global showpiece.
Cameroon refused to capitulate and were level nine minutes later when Allan Nyom squared for Joel Matip to side-foot into an empty net and momentarily silence the home fans.
Shouts of "Brazil! Brazil!" then rang out and the hosts were back in front in the 35th minute when Neymar ran at the defence and clipped a low shot past a wrong-footed Charles Itandje in the Cameroon goal.
Brazil made a similarly brisk start to the second period and David Luiz popped up on the left wing in the 49th to chip the ball to the far post for Fred to head home.
Neymar came off to a rapturous reception and was replaced by Willian in the 71st minute before Fernandinho clipped the ball into the corner after a well-worked move six minutes from time to complete an impressive win for the tournament favourites.
"The main thing today wasn't the result but the way the team played, getting back the spirit that we had in (last year's) Confederations Cup," Fernandinho said in a television interview.
"In the first two games of the World Cup we missed that a bit," added the midfielder.
Cameroon, whose campaign has been wrecked by infighting and ill-discipline, depart having lost all three matches, conceding nine goals and scoring one.
Coach Volker Finke said he had been reasonably pleased with the Indomitable Lions' performance in the first half but criticised his players for not maintaining their concentration.
"It's not the first time we haven't focused for the whole 90 minutes, we need to find the reason for this," Finke told a news conference.
"Three times we had control of the ball and we lost it and those goals were unnecessary," added the German.
"There were certain things that were quite positive but it wasn't enough for the World Cup. We need to look at reality and as we are it's not enough for this competition." (Additional reporting by William Schomberg, Brian Homewood and Patrick Johnston, editing by Ed Osmond)