The Netherlands play surprise package Slovakia in a round of 16 match on Monday, wary of a team spirit that saw the unheralded side beat defending FIFA World Cup champions Italy in the group stage.

The two-time finalists were themselves unbeaten in the group phase, brushing aside Denmark, Japan and Cameroon. Slovakia drew with New Zealand and lost to group-winners Paraguay before trumping Italy to spectacularly claim their runners-up spot.

"Slovakia will be tough," warned Dutch striker Robin van Persie. "They showed really good spirt and hung in there against Italy and it was a great result for their country. So far, it's looking good for us, but we can still improve on bits and pieces." Dutch coach Bert van Marwijk added: "This is an opponent we must not underestimate. We cannot be nonchalant."

This is an opponent we must not underestimate. We cannot be nonchalant.

Robin van Persie, Netherlands forward

Although the Dutch notched up three group phase wins - a feat matched only by Argentina, van Marwijk warned they could ill afford to let teams back into games through sloppy play, as was the case against Cameroon. "That period of negligence we had, we cannot afford that again," he said. "It's a bit of a lesson for the next match."

Slovakian striker Robert Vittek, who scored two goals in his team's win over Italy, said that the game against the Azzurri had "really pushed the limits of Slovak football".

"Beforehand we couldn't have dreamt about this, I'm so happy, we showed everything that we're capable of in achieving this," he said. "We've got nothing to lose, we came here as outsiders and newcomers and we wanted to surprise people. We've done it once and we hope to do it again. We hope to play against Holland in the way we played (against Italy), but they are one of the favourites."

The Netherlands were boosted by the return against Cameroon of star winger Arjen Robben, who made his South Africa 2010 bow as a late substitute after missing their opening two matches with a hamstring injury. If there were any lingering doubts over his injury, Robben erased them in emphatic style with a trademark contribution to the Netherlands' winning goal, slamming a shot against the post with Klaas-Jan Huntelaar burying the rebound.

"We made it clear at the start that we would be taking this tournament one challenge at a time, and now we will focus on Slovakia and Slovakia alone," said Robben. "I'm already looking forward to it."

The winner of the second round match at the Moses Mabhida Stadium will face a tough quarter-final against the winner of the Brazil v Chile play-off.