Slovenia play their Group C opener against Algeria in Polokwane on June 13, meet United States in Johannesburg five days later and take on England in Port Elizabeth on June 23.
"It was a good performance and I was especially pleased for (striker) Milivoje Novakovic to score two excellent goals from free kicks but it was only a friendly and World Cup games are going to be a different story," Kek told Reuters.
"I am also happy that the injury to Zlatan Ljubijankic (ankle) is not a serious one and he will be fit for the opening game against the Algerians.
"The most positive thing was the fantastic farewell we got from a capacity 12,000 crowd in Maribor. They were as vociferous and passionate as ever."
Novakovic took his international tally to 16 goals in 38 games with a pair of superbly taken free kicks while Andraz Kirm added the third in an eventful first half on Friday, with Rory Fallon netting New Zealand's equaliser.
The Slovenians looked dangerous every time they came forward but were often left exposed at the back and Kek said they needed to improve defensively for the June 11-July 11 finals.
"There is room for progress in several departments, especially when we don't have the upper hand but overall I am satisfied with our buildup for the World Cup," he said.
"We can't wait to arrive in Johannesburg on Monday morning and the lads are really raring to go."
(Reporting by Zorn Milosavljevic in Johannesburg; Editing by Jon Bramley)