Alonso finished a creditable third in the Singapore Grand Prix last weekend, and could have been forgiven a grin within his helmet when he saw nearest championship challenger Lewis Hamilton retire early with a malfunctioning gearbox in his McLaren.
But the Spaniard has gone four races without taking the checkered flag, and with Red Bull's Vettel winning the Marina Bay night race, another formidable challenger replaced Hamilton in second place in the standings.
"In the end it went well but we definitely can't go on like this," Alonso said.
"It can't always be the case that my closest rival retires, as has happened in the last two races, and we can't think of carrying on to the end of the season with qualifying sessions like (Saturday) when our performance was almost a second off the best."
Ferrari team boss Stefano Domenicali agreed that improvement was necessary, particularly given the nature of the tracks in the remaining six races, with South Korea and Abu Dhabi requiring similar car set-ups.
"Clearly we need to make a step forward in terms of performance, because we cannot rely purely on the misfortune of others," Domenicali said.
"Having said that, we mustn't over-react as it's better to bring a few updates that work rather than bringing too many. This is the area where we need to improve and it will be one of our priorities in the coming days."
For Vettel, the Singapore win provided renewed hope of becoming just the third man — after Juan Manuel Fangio and Michael Schumacher — to win three straight drivers' championships.
It was only his second win of the season, but with the remaining circuits tailored toward a more nimble car, and not requiring the outright speed the Red Bull lacks, the German now looms as Alonso's chief rival.
"It's looking better than before," Vettel said. "We have a lot of races left, the car seems to be competitive and we just have to use the momentum and keep pushing for these last races and see what happens."
Hamilton's season is continuing on its feast-or-famine pattern, with his past five races yielding two wins and three non-finishes. The Briton was not distracted by ongoing rumours about the possibility of him leaving McLaren for Mercedes, and showed that by setting pole position and comfortably leading the race until the gearbox failed on lap 23 of 59.
That non-finish meant Kimi Raikkonen retained his third place in the standings, despite the Lotus driver not having won a race this season. No man has ever managed to take the title without winning a race, but if he keeps toting up the points while those above him fail, the Finn can keep his chances alive.
McLaren's Jenson Button kept a pulse in his faint title hopes by taking second place in Singapore, while Red Bull's Mark Webber is above Button in the standings but had another disappointing weekend, crossing the line in 10th and then being dropped out of the points to 11th as a penalty for an overtaking move off the limits of the track.
The next race is at Suzuka in Japan on Oct. 7.