Testing times at Mercedes as rivalry between friends Hamilton and Rosberg escalates into feud

Mercedes driver Nico Rosberg of Germany sprays champagne after winning the Monaco Formula One Grand Prix, at the Monaco racetrack, in Monaco, Sunday, May 25, 2014. Nico Rosberg won the Monaco Grand Prix from pole position on Sunday to take the overall championship lead from his teammate Lewis Hamilton, who finished second to give Mercedes a fifth straight 1-2 finish. The German driver clinched his second victory of the season and fifth of his career, making a strong start and holding off Hamilton to repeat his maiden GP win from pole here in Monaco last year. (AP Photo/Luca Bruno) (The Associated Press)

Mercedes driver Lewis Hamilton of Britain indicates on the podium after receiving the trophy for his second place after the Monaco Formula One Grand Prix, at the Monaco racetrack, in Monaco, Sunday, May 25, 2014. At right in background Mercedes driver Nico Rosberg of Germany is flanked by Princesse Charlene. Nico Rosberg won the Monaco Grand Prix from pole position on Sunday to take the overall championship lead from his teammate Lewis Hamilton, who finished second to give Mercedes a fifth straight 1-2 finish. The German driver clinched his second victory of the season and fifth of his career, making a strong start and holding off Hamilton to repeat his maiden GP win from pole here in Monaco last year. (AP Photo/Luca Bruno) (The Associated Press)

At last, Formula One has a heated rivalry again. Better still, it's in the same team and there are 13 races left for it to develop.

The dominance of Mercedes, which has swept all six races and all six pole positions so far, prompted fears that this season was becoming even more predictable than the last, when Sebastian Vettel won the final nine races and Red Bull crushed everyone.

Then, at last weekend's Monaco GP, a feud erupted out of nowhere between Mercedes drivers Lewis Hamilton and Nico Rosberg to add some much-needed spice to a dull campaign.

Hamilton has won four races this season, but Rosberg captured Sunday's race from pole for his second victory and reclaimed the overall championship lead with 122 points to 118 for his teammate.