It's been a while since there's been this kind of excitement early on in a Formula One season.
There hadn't been three different winners in the first four races since 2013, the year before new engine rules that led to Mercedes' dominance.
Mercedes won this year with Lewis Hamilton and Valtteri Bottas, but Ferrari joined the fight with two victories by Sebastian Vettel.
The championship battle could get even tighter as F1 returns to Europe this weekend for the Spanish Grand Prix in Barcelona, where Red Bull is expected to get a big jump with new upgrades.
"There are two top teams fighting for both championships and I expect Red Bull will also eventually join the club," Mercedes boss Toto Wolff said.
"The small margins we are seeing this season are demonstrated by the closeness at the top of the drivers' championship and even more so by the one-point advantage we have in the constructors'. This fight will continue on to the end of the season and we will be prepared for that battle."
Vettel has a nine-point lead over Hamilton in the drivers' standings and is 23 points in front of Bottas. Ferrari teammate Kimi Raikkonen is fourth, ahead of Red Bull's Max Verstappen, who last year won in Barcelona to become F1's youngest race winner at age 18.
Verstappen's Australian teammate Daniel Ricciardo said he was looking forward to improvement with the upgrades this week to Red Bull.
"I hope the upgrade will give us a chance to really fight with Mercedes and Ferrari or at least get us closer," said Ricciardo, who finished only two races this season.
"It's a good feeling for everyone when these upgrades work."
Wolff said Mercedes had to face this new scenario after dominating for three seasons.
"This inter-team battle is a totally different situation than what we have seen over the last three years. You simply need to adapt to the challenge and that's what we are doing, playing the hunter as well as being the hunted."
Nico Rosberg, winner of the first four races in 2016, won the title last season with Mercedes, while Hamilton won the previous two championships.
Bottas replaced the retiring Rosberg and won his first career race two weeks ago at the Russian GP.
"We expected Valtteri to develop through every single race and step up his performance and he's shown that," Wolff said.