Polasek won the men's title on the 100 metre hill at the Utah venue, home to the Salt Lake City 2002 Winter Olympics.

He recorded an effort of 97m to strike gold, with Alex Insam of Italy leaping to silver.

Germany's Constantin Schmind completed an all-European podium with the bronze.

"It feels great to be junior world champion now," said Polasek.

"I came here with big expectations and I’m glad I was able to fulfill them. 

"In last year’s Junior World Championships I was fourth and I expected to be better this time. 

"So I’m extremely satisfied."

Malsiner managed an effort of 95.5m en-route to claiming the women's title.

Slovenians Ema Klinec and Nika Krizna were second and third respectively.

Elsewhere, Vladislav Vechkanov led a Russian 1-2-3 in the men’s 10 kilometres cross-country freestyle.

He won by 7.9sec over team-mate and silver medalist Egor Kazarinov, with Yaroslav Rybochkin taking bronze.

"I arrived at the finish and actually I didn’t think I would win gold," said Vechkanov. 

"So I pushed knowing that I would be in top three, but not winning. 

"I started really slow. 

"Then on the second loop I tried to increase my speed. 

"On the last uphill I tried my best to make it to the finish line without any strength and I hoped I would be in the top three. 

"But now I’m first."

The women's 5km race was won by Sweden’s Ebba Andersson who picked up the third gold medal of her career.

The silver medallist was Marte Maehlum Johansen of Norway as Russia’s Mariya Istomina bagged bronze. 

Tomorrow will see the  men's under-23 15km freestyle, and the women's under-23 10km freestyle.

A team Nordic combined competition will also be held.