The 29-year-old, who has won the last three Tours, began the 15km freestyle pursuit with a lead of 50.3 seconds at the top of the overall standings and that wasn’t to be bridged in Italy.
Kowalczyk skied from Cortina to Toblach completely on her own recording a winning time of 37.15.1 minutes to add to her victory on the second stage, also a pursuit, in Oberhof.
With four of the seven stages now complete only Kowalczyk and American Kikkan Randall have tasted victory although the Polish cross-country skier isn't guaranteed a fourth straight title.
For 2008 winner Charlotte Kalla produced a storming performance in the second pursuit of the Tour de Ski, making up well over a minute to finish second 18.3seconds behind Kowalczyk.
Norwegian Therese Johaug, second overall prior to the race 50.3seconds off Kowalczyk, appeared on course for second but was beaten by the flying Kalla and ended third 0.4 further adrift.
With bonus seconds added, Kowalczyk earns 15 for finishing first, Kalla ten for second and Johaug five for third, the defending champion leads the Tour de Ski by 23.3seconds.
Kalla occupies second and Johaug third with Kowalczyk satisfied with her cushion at the top ahead of the 3.3km classic individual in Toblach on Friday.
"It was very hard and I am so tired now but it was a really good win," said Kowalczyk. "For me it was the most important race and 23 seconds is a good gap."
- Sports & Recreation
- Charlotte Kalla