In total, he increased his advantage of the Team Sunweb rider by nine seconds, but it was Froome who suffered even more on the stopwatch.
"The last few days I felt really good, which is a good sign", said Martin. I tried to ride it like a time trial, but the altitude got me in the end.
While Movistar's Nairo Quintana won atop the Col du Portet to move back into the top five, Froome lost contact with the main group of contenders around two kilometres before the summit. Dumoulin constantly remained a threat, but never close enough after losing time in the first week due to a puncture and time penalty for drafting.
Four-time champion Chris Froome and current Yellow Jersey holder Geraint Thomas were among the cyclists forced to pull over and pour water in their eyes. The same Brit beat Dumoulin to second place when they both raced the Giro d'Italia last month.
Froome came off his bike and fell to the ground before getting up, looking to be very angry with the policeman in question. Dumoulin attacked next, but was again followed by Thomas.
Sir Dave Brailsford, Team Sky's principal, praised Froome's reaction to his disappointment, adding that the way he and Thomas have worked together during this Tour was deserving of a huge amount of credit.
Quintana said: "I'm happy for the win".
The Quick-Step Floors rider, who already prevailed in the 10th stage in Le Grand Bornand, whizzed past Adam Yates six kilometres from the line after the Briton had hit the asphalt in a left-hand curve in the final descent.
"I didn't want him to have a bad day like he did but it just gave me confidence knowing someone of Froomey's stature was struggling, and I just knew I would be able to respond to the attacks". "I can only be satisfied with that ride".
"My intention was never to criticise, just to draw some attention to the fact that I was getting pretty anxious about our guys", Brailsford added.
It could, however, also open the door for a challenger to emerge and Dutchman Tom Dumoulin is one of those lying in wait for the top two to slip up.
It was a gift, but Alaphilippe didn't care as he cruised to his second stage win of this year's Tour.