Daniel Ricciardo says that his current Red Bull team mate Max Verstappen is the best he's ever had.
That puts the Dutch driver ahead of four-time world champion Sebastian Vettel, who raced alongside him in 2014.
"I'm not saying I've had it easy in the past," Ricciardo told Motorsport.com "But I think he's the first driver who can challenge me."
Other previous team mates have included Daniil Kvyat and Jean-Eric Vergne, as well as Narain Karthikeyan and Vitantonio Liuzzi from his maiden season at HRT.
"In the past, if I've done a high-speed corner and I've taken it flat-out for example, I've never had someone who can get there the same way.
"Max would at least go out there and try it," he explained. "He's been able to match stuff easier than some other guys have."
Ricciardo finished ahead of Verstappen by 32 points in last year's drivers championship. However, Verstappen won two races during the year compared to just one for the Australian.
Ricciardo admitted that his team mate's "qualifying improved" in 2017. The youngster beat Ricciardo 13 times out of 20 qualifying sessions in 2017
"I know if I made a little mistake in the past, maybe I could end up ahead still in qualifying," Ricciardo said. "Now, if I make a mistake, he's in front.
"It's the same if he doesn't quite put a perfect lap together - I'm in front.
"This is why I would say he's the better teammate," he added. "We've both raised our game. We can't afford to put a wheel wrong."
In total, Verstappen was ahead of Ricciardo for 371 laps over the course of the season. Ricciardo was in front for just 156 laps. However both men suffered from engine unreliability, leaving both of them frustrated.
Verstappen went on to finish ahead of him on five occasions where both men finished. Ricciardo only pipped Verstappen twice.
"If we were to split the races, we both had an even amount of good races," Ricciardo insisted. "His good days probably looked better because they weren't good days for me."
Assuming that Red Bull and engine providers Renault give them a strong package in 2018, Ricciardo says they will be "relatively" evenly matched.
He predicted a close fight for team honours this season - and hopefully also for the world championship.
"I believe this year we will close the gap," he predicted. "Is it enough to fight for a title? I think we can certainly get close."
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