The Bayern Munich man believes that his team-mate, who topped the scoring charts in 2010, has proved that he has what it takes to make the difference for Joachim Low's side
Muller grabbed a hat-trick as Die Mannschaft swept aside Portugal 4-0 in their Group G opener in Salvador on Monday, in what was the 24-year-old's 50th cap for his country.
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"Thomas Muller's performance was outstanding," Gotze told Fifa's official website.
"Now he's got three goals. That was very, very important, both for the team and for Thomas himself.
"He's a top-quality player and we saw that [on Monday]. He's clinical in front of goal and can score from nothing. The ability to do that, especially at a World Cup, can be decisive."
Muller, whose five goals and three assists at World Cup 2010 saw him edge past Diego Forlan, David Villa and Wesley Sneijder to the Golden Boot award, now has 20 strikes for his country.
Germany will continue their group-stage campaign on Saturday when they face Ghana in Fortaleza.