Cross-country skier Alex Harvey finished a disappointing 21st in Wednesday's 15-kilometre classic mass start, dropping the Canadian to 10th spot in the Tour de Ski after the fifth stage.

The 27-year-old had moved to eighth following Tuesday's 15th-place performance in the men's 1.2km sprint in Oberstdorf, Germany.

Alexey Poltoranin of Kazakhstan topped the field of 63 on Wednesday, edging Dario Cologna of Switzerland in a photo finish.

Poltoranin finished in 35 minutes 35.9 seconds, one-tenth of a second ahead of Cologna, who was 0.6 seconds ahead of Francesco de Fabiani of Italy.

"I hope for top 10 in Toblach [on Friday] and I will fight for the third place in the Tour de Ski," Poltoranin told reporters.

Harvey stopped the clock in 36:30.5 while Devon Kershaw and Ivan Babikov also competed for Canada on Wednesday, finishing 29th (36:48.3) and 34th (37:07.4), respectively.

After five of eight races in the Tour de Ski, Martin Johnsrud Sundby still leads Norwegian teammate Petter Northug Jr. despite finishing 23rd.

Therese Johaug beat Ingvild Flugstad Oestberg in the women's 10km mass start to cut her Norwegian teammate's lead in the Tour de Ski to just 12.2 seconds.

Norwegians completed the top four, with Johaug winning in 26:37.6, 9.9 seconds ahead of Oestberg.

"I am happy to gain some seconds. It will be a tough fight with her all the way to the top of Alpe Cermis," said Johaug, referring to the last of the eight-race series at Val di Fiemme in Italy.

Heidi Weng was 19.7 behind in third, followed by Ragnhild Haga and Anne Kylloenen of Finland, both more than a minute behind.

Weng is 2:33.1 behind Oestberg in the Tour de Ski standings.

Three races remain in the series, with action resuming in Toblach, Italy, on Friday, when individual races are scheduled.

With files from The Associated Press