"My shape is getting better by the day, I'm proud that I won again today", said Groenewegen, who won the final stage on the Champs Elysees previous year.
Defending champion Chris Froome crossed eight seconds after Martin in 18th. Once they're through that, the riders will swoop down and across the Eure river with 1K to go.
Greg Van Avermaet held on to the yellow jersey he grabbed on stage three and doubled his lead over Geraint Thomas to six seconds by winning an intermediate bonus sprint. '"With 200 metres to go I saw the gap and I was going to the finish line".
The Tour hadn't returned to the Brest to Mûr-de-Bretagne since.
"I just keep trying, our backs are against the wall all the time here".
"I had good sensations but nothing outstanding, I was at my maximum".
It's not a day that should affect the General Classification, as overall leader Greg Van Avermaet should have no trouble with the finish.
The longest stage of the 2018 Tour de France played out exactly as expected - nobody wanting to go clear, and the pace low in the peloton.
Since the route was announced in October, this 156.5km stage nine over the cobbles of northern France to Roubaix had been circled as the wildcard which could deliver a jolt to the race, and it did not disappoint.
"I'd like to thank Greg (Van Avermaet) because he did me a favour when he went for it, I don't know if he did it on goal but he dropped a lot of people", said Sagan, who has tightened his grip on the points classification's green jersey.
"I have my own style", he said when asked about his similarity to the veteran Manxman with 39 stage wins under his belt.
"I'm hoping still to improve", the Slovakian said.
Sagan, who was been guilty of watching Gaviria a little bit too much in the recent stages, opened up his sprint early today and was overhauled by Groenewegen, Andre Greipel (Lotto-Soudal) and the Quick-Step rider.
Dumoulin said his bike broke when he knocked into Bardet near the foot of the second of two two-kilometre ascents up the Mur de Bretagne to the finish line.
The Dutchman, who rides for LottoNL-Jumbo, moved before his rivals as the 231-kilometer (143-mile) stage from Fougeres to Chartres ended in a bunch sprint.
England players hailed as ‘Heroes’ by British media after World Cup heartbreak
Croatia , in their first semi since 1998, levelled through Ivan Perisic after 68 minutes and then looked the more unsafe side. Liverpool 's Lovren is set to come up against Tottenham Hotspur 's Harry Kane when Croatia and England meet on Wednesday.