Four rounds into the 2018 MotoGP season and the top Yamaha rider is second in the world championship, with two podiums and one pole position.

But that rider isn't Valentino Rossi or factory Yamaha team-mate Maverick Vinales.

Instead, it's satellite star Johann Zarco who is taking the fight to Honda, which has won three of the four races this season courtesy of Marc Marquez (2) and Cal Crutchlow (1). The other victory was by Ducati's Andrea Dovizioso, with Yamaha winless for almost a year.

Zarco - runner-up in two of the four races - sits just 12 points from reigning champion Marquez after a fortuitous second place in Jerez, where Dani Pedrosa, Jorge Lorenzo and Andrea Dovizioso were eliminated in a single turn.

But even if they had stayed on, Zarco - despite older equipment and a fraction of the factory team's resources behind him - was quicker than the gripless Movistar riders in practice, qualifying and the race.

The Frenchman then set the fastest lap time of all at Monday's official post-race test.

MotoGP Champion Marc Marquez interviews - himself

It's not just media and fans raising eyebrows, even world champion Marquez finds the Yamaha situation 'strange'.

Adding to the conundrum is that Yamaha appeared to make little attempt to retain Zarco, who has been snapped-up by the factory KTM team for 2019, having turned down interest from Honda, Suzuki and Ducati.

"It was a strange first four races. Everything happened," Marquez said, when asked who he sees as being a consistent title rival.

"We will see during the European races, but for me Zarco will be very strong this year and Dovizioso. Dovizioso was fast [in Sunday's race] and he will be fast all the season.

"Then we will see what's going on with [factory] Yamaha riders and my team-mate [Dani Pedrosa]. Of course my team-mate now is far in the championship, but there are still many remaining races.

"But with the Yamaha riders it's strange because Johann is [the leading] Yamaha rider."

Vinales is third in the standings, eight points from Zarco. Rossi is sixth and 18 points behind the Monster rider, not helped by a non-score in Argentina after being bumped wide by Marquez.

But even without that incident, as at Jerez, both Rossi and Vinales were off the pace of Zarco, who seems to find grip on tracks where the factory riders are left in a spin.

Yamaha MotoGP 2018 Team

Asked what he can see Zarco doing differently compared to Vinales and Rossi, Marquez replied:

"Of course there are different riding styles between them. Maybe the most similar is Johann and Valentino. Maverick has another riding style. But it's not worse or better. I mean it's different and sometimes it's better, sometimes it's worse.

"But it's strange [that Zarco is the fastest] and I can't answer this because even they cannot answer and they have all the data. They have everything."

But as a 'neutral observer'…

"From a neutral observer, Yamaha lost a really good rider - I mean, he's going to KTM!" Marquez responded. "At the moment he's the fastest one.

"Of course the experience of Valentino is really good and Vinales has the speed. But at the moment Zarco is doing a great job."

Round five of the world championship will be Zarco's home round at Le Mans - the first of 15 remaining chances for Zarco to become the first satellite Yamaha rider to win a four-stroke MotoGP race.

Zarco was just 0.337s from victory at Valencia last year, then beaten by a mere 0.251s in Argentina this year.