After the opening Grand Prix of the 2015 Formula 1 season, the script for the year already looked to have been written. Having dominated in 2014, winning constructors’ and drivers’ titles, Mercedes appeared to have only increased their advantage over the winter. World champion Lewis Hamilton finished nearly 1.5 seconds ahead of the quickest non-Mercedes in qualifying, and he and teammate Nico Rosberg finished more than 30 seconds in front of their rivals in the race in Melbourne.

There was talk, from the head of Red Bull and even Formula 1 chief executive Bernie Ecclestone, that Mercedes needed to be reined in. The feeling among many was that their advantage was so great that the competitiveness had been drained out of the sport.

Then, Ferrari and Sebastian Vettel did what few, if any, expected. In just his second race for Formula 1’s historically most successful team, the four-time world champion stunned Mercedes by not just winning the Malaysian Grand Prix, but doing so, as he described it, “fair and square.” There were no Mercedes mechanical failures, no accidents or freak weather, Vettel’s Ferrari had the pace to beat Hamilton’s Mercedes to the checkered flag.

“I’m speechless,” Vettel said after the win. “Obviously a big change over the winter and the welcome the team gave me is just fantastic. I’ve only done two races but it’s a great atmosphere. I’m very, very happy. Proud of today, we beat them fair and square. A great achievement, we have a great car. Plenty of positives and I guess that’s why it is a bit emotional.”

Mercedes head of motorsport Toto Wolff later revealed that the pace shown by Ferrari was “worrying.” Yet the big question remains whether this was a one-off, or if Vettel and Ferrari can now make it a far more intriguing championship race than had appeared likely.

After years in the doldrums, which prompted Fernando Alonso to depart after last season, Ferrari have undoubtedly made great strides, even since Australia. Still, the key difference between the two Grands Prix was the rise in temperature in Malaysia. And in the heat, Ferrari managed their tires much better than Mercedes, crucially requiring one fewer pit stop. The temperatures are unlikely to be as high again this season, certainly not on a regular basis. So the question remains whether Ferrari can remain as competitive in cooler conditions, starting with the race in China next weekend.

“I think ultimately my assumption is that this weekend the heat got to us with the tires and it will be a lot cooler at the next race, so I hope that we pick up our pace a bit more,” was Hamilton’s verdict.

Certainly Mercedes remain favorites to get back to winning ways in Shanghai. And even Vettel expressed his feeling that, while Ferrari have shown potential, the champions remain the team to beat.

“For sure we would like to be in that situation for every race to come from now on, which is also our target,” he said in an interview with the official Formula 1 website. “On the other side we have to be realistic as well, as they had a very big gap in winter testing and in the first race, which does not just evaporate. Our target has to be that the gap between them and us keeps getting smaller, as the gap will still be there.”

Mercedes now, though, know that they will not be able to rest on their laurels, and they will have to improve to remain ahead of Ferrari. Vettel’s win could be a particular warning for Rosberg. The German has won just one of the last 11 races dating back to last year, having failed to get the flying start to 2015 he arguably needed to show that he has what it takes to challenge Hamilton over the long term. Now, already being comfortably out-performed by his teammate, Rosberg is in danger of being shown up by his countryman.

That still remains some way off, but he and the rest of Formula 1 should be enlivened by Ferrari’s most unexpected triumph.