SAKHIR, Bahrain -- Mercedes boss Toto Wolff has likened the current battle at the front of the field in Formula One to the rivalry between tennis players Roger Federer and Rafael Nadal.

After Lewis Hamilton and Sebastian Vettel scored a victory each at the opening two rounds of the season, Valtteri Bottas joined the emerging battle for this year's title by taking pole position in Bahrain. After three years of a tense, and at times poisonous, battle between Hamilton and his ex-Mercedes teammate Nico Rosberg, Wolff says the emerging three-way battle has a different feel.

"I think the Nico and Lewis situation was very special because they go back a long time, it was a lot of baggage, some of it we know, some of it we will never know, and it got quite intense and controversial at times," he said. "I don't feel that same stress in the relationship between the two of them.

"Somehow between Vettel, Valtteri, and Lewis I feel a little bit of a... I feel there's a lot of respect. Whether that will last? I hope so.

"I think as a driver you never want to lose and you never want to lose against your teammate, but I can see there is a lot of respect for each other [between Hamilton and Bottas]. I see that not only in the car, but when they engage with each other.

"It reminds me -- with Sebastian also in the mix -- it is very sportsmanlike, like a Federer/Nadal situation -- they don't want to be beaten by the other guy but somehow there is a respect for the other person."

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It is the first time Bottas and Hamilton will line up on the front row of the grid as Mercedes teammates -- and at the same venue where they had a first corner collision last year -- but Wolff is looking forward to the race between his two drivers.

"I would rather have them starting P1 and P2 and give me the jitters throughout the race because at the end it is what we want to see. If you are two drivers that are separated by a couple of thousandths you can expect close racing. It is not very comfortable but equally very exciting.

"It's clear that when you have two drivers at the very front it is always more stressful than when they're separated, but Formula One needs that and it is what we want as well. So having those guys battling it out is just what we all want."

The on-track battle between Rosberg and Hamilton over the past three years was regulated by Mercedes' 'Rules of Engagement' -- a document drafted by the drivers and top management ahead of each season to define what is acceptable when racing wheel to wheel. Wolff said a similar document exists between Bottas and Hamilton, but it is now filed under a different name.

"We did it like we do it every year, we sat down and copy and pasted [the previous document] and added things and changed things -- like where we could have some a better job, like in Abu Dhabi [last year].

"We went through the document with them at the beginning of the season so it is pretty much the same. We have changed the name of the document, it is not the 'Rules of Engagement' anymore, it is now the 'Racing Intent', it sounds more positive."