Chris Froome expects to be on his best form in the final week of the Tour de France as he fights to hold on to the yellow jersey in the closest battle this race has ever seen.

Just 29 seconds cover the top four as Team Sky's Froome leads by 18 seconds from Italian national champion Fabio Aru, with Frenchman Romain Bardet a further five seconds back in third and former Sky rider Rigoberto Uran of Colombia looking ominous in fourth.

Dan Martin is next in fifth, 1.12 down, but he has been gradually clawing back seconds since his lost over a minute in a fall last week.

The race will head towards the Alps after Monday's rest day, with stages on Wednesday and Thursday potentially decisive before Saturday's time trial in Marseille.

Three-time Tour winner Froome is used to beginning the final week of the race with a decent cushion to defend, but struggles in the Pyrenees saw him temporarily surrender yellow and left his rivals bunched up behind him.

However, after taking a different approach to his preparation this year, Froome believes he is just about to peak.

"I certainly feel as if I'm on an upward curve," the Kenyan-born Briton said. "I came in with the least amount of race days ever coming into a Tour de France. I really do feel as if I'm coming up and the last few days have been evidence of that.

"I had a bad day in the Pyrenees about a week ago but hopefully I'm on track to be at my best in the last week."

Ireland's Dan Martin, with Foome behind him in the distance

Froome lost yellow to Aru on an epic stage 12 to Peyragudes on Thursday but reclaimed it 48 hours later.

However, he had to be at his best just to retain it on Sunday as a broken spoke on his bike left him a minute down on his rivals at the foot of the Col de Peyra Taillade, and the 32-year-old had to go into the red just to save the day as Bardet's AG2R La Mondiale team drove the race on.

The route for this year's Tour is a big part of the reason everything is so close. There are only three summit finishes and very few time trial kilometres - with most of them still to come next Saturday.

Battles against the clock tend to strongly favour Froome, but he will not be lulled into relying on the time trial to claw back time knowing that Cannondale-Drapac's Uran poses a strong threat in such a setting.

"Rigoberto is more the dark horse," Froome said when asked about his main rivals. "He slips under the radar a little bit. He's probably the strongest time trialist of this group of GC contenders so with Marseille in mind he's a big threat."

Aru took yellow from Froome in the Pyrenees, and he also impressed by winning on the first summit finish to La Planche des Belles Filles, only to give up the race lead when he faded badly on the finish to Rodez on Saturday.

There is also a sense it is Bardet and Uran who pose the bigger threats due to the weakness of Aru's Astana team.