Chris Froome (Team Sky) believes the Tour de France’s first real GC battle to La Planche des Belle Filles on stage five has shown who his main challengers for the race’s overall victory are likely to be, as the Briton moved into the race lead for the first time in 2017.

Froome, who is chasing his fourth overall victory in the Tour, finished third on the stage – 20 seconds behind winner Fabio Aru (Astana), with the result on the day shuffling the overall GC.

The Team Sky rider took the maillot jaune from team-mate Geraint Thomas by 12 seconds. Aru moved up to third, Dan Martin (Quick-Step Floors) fourth and Richie Porte (BMC Racing) in fifth – the latter 39 seconds back.

>>> Fabio Aru wins on summit finish of Tour de France stage five as Chris Froome takes overall lead

“It gives us a glimpse of where everyone is at,” Froome said after the stage. “When I made my move in last two kilometres, seeing that it was Richie, Dan Martin and [Romain] Bardet were able to follow me. That was an indication of who has more to give on the climbs, and Fabio, of course, considering he was out front.

“I think it’s going to be a big battle. That’s just what the organisers wanted. It’s a more open race, that’s the way it looks for sure.”

With Thursday and Friday’s stages likely to end in bunch sprints, the next test for the GC riders is Saturday’s stage eight to Station des Rousses in the Jura Mountains. Yet Froome believes the race is still wide open, with Quick-Step’s Dan Martin among those who impressed on La Planche des Belle Filles.

“This kind of final suits some guys better than others, like Dan Martin; we expect him to be strong in those punchy finishes, and he did a great ride today,” Froome continued. “You have to look at GC; it’s a really close race. It’s still very open. We have a lot of racing ahead of us.”

Watch: Tour de France stage five highlights

Despite Sky having the yellow jersey at the start of the day with Welshman Thomas, it was BMC Racing doing most of the work on the flatter part of the day chasing down the eight-man breakaway up the road.

Sky hit the front of the peloton when the final 5.9km climb – where Froome won his first Tour stage in 2012 – approached, with six riders still to work for Froome. Michal Kwiatkowski rode the first 1.5km, before Mikel Nieve took over, then Thomas. Froome attacked shortly after, causing Alberto Contador (Trek-Segafredo) and Nairo Quintana (Movistar) to drop out of the select lead group of riders.

Though Contador and Quintana managed to claw back towards the front before the finish line, they were the two major contenders to lose time on the stage – with the latter dropping 14 seconds to Froome. Yet Froome said he didn’t think there were “really significant gains and losses”.

>>> Five talking points from stage five of the Tour de France

“The team’s been fantastic so far,” Froome said after the stage, wearing the yellow jersey. “The team confirmed it, having the numbers in the final climb, with six riders in the final. No other team had those kinds of numbers. I think we can take a lot of confidence out of that.”

While Froome said BMC’s tactic of driving the pace for much of the stage shows the level of confidence the squad has in Porte, it also left them without any riders on the climb at the crucial part of the race.

“I think they showed initiative and intent that they wanted to win the stage with Richie. If anything, they were left a little bit short on the final climb for Richie,” Froome continued.

“If they did want to win the stage, they could have done with one or two more climbers to close the gap to Aru on the flats before the final kick. They did a good job in showing their confidence for Richie.”