Daniel Martin of Ireland won an uphill finish to claim Stage 6 of the Tour de France on Thursday, while Greg Van Avermaet kept the yellow jersey for a third consecutive day.
"I tried to win the stage but it was pretty complicated", Van Avermaet said.
"I knew I wouldn't make it back so it was about limiting the time loss", Dumoulin said.
The pair have two stage wins each from the first five and Sagan had predicted Tuesday the Colombian might struggle with the climbs.
The pair are 13th and 14th, one minute two seconds behind yellow jersey Greg van Avermaet, and one second ahead of Dumoulin. "I thought the corner was closer to the finish than it really was".
"If tomorrow is like that and all goes well on the cobbles on Sunday, it would be great to go into the rest day with the yellow", said Van Avermaet, who will be helping GC contender Richie Porte to keep out of trouble on the Roubaix stage.
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In the fifth stage, he mastered the final ascent excellently, and he did not start sprinting too early.
Chris Froome went headfirst into a grass verge and ended nearly two minutes off yellow but could call Sunday a success as he survived a chaotic day on the Tour de France when others were not so lucky. The French rider with the Wanty-Groupe Gobert team established an advantage of more than eight minutes _ the biggest breakaway lead in this year's Tour _ before being caught by the pack with 90 kilometres to go.
Astana's Jakob Fuglsang did not fall foul of the race jury despite enduring a similar chase back on himself, earlier in the stage.
Stage 8 on Saturday covers a slightly more challenging terrain over 181 kilometers from Dreux to Amiens but again should set up well for sprinters.
Dutchman Groenewegen showed impressive power to burst clear of Quick-Step Floors' Fernando Gaviria and world champion Peter Sagan of Bora-Hansgrohe at the top of a gradual climb to the finish of the 231-kilometre stage from Fougeres. With this victory, the Slovakian leads the Tour's overall classification by 33 points, and tightens his grip on the green jersey.
Groenewegen grew up in a cycling environment as his grandfather was a bike manufacturer and his boyhood coach was Jean-Paul van Poppel, victor of nine sprint finishes at the Tour de France.