World champion Fernando Alonso expects his commanding early season lead to dwindle as his rivals make improvements to their cars as the season progresses.
Renault design boss Pat Symonds has said he expects Ferrari, on Bridgestone tyres, to win at Imola on 23 April.
"We have to take our opportunities and win these races now," said Alonso. "The other teams will improve and be similar to us or quicker than us.
"Imola is a different challenge and it will be more difficult than ever."
Alonso has won two of the first three races this season and has already amassed 28 points, 14 more than team-mate Giancarlo Fisichella and McLaren's Kimi Raikkonen.
Alonso puts Button in his place
He looked totally in control in winning the Australian Grand Prix, despite four safety car interventions and carnage all around him.
Ferrari, meanwhile, came away from Melbourne with no points and are well behind Renault in third in the constructors' standings.
Felipe Massa crashed out on the first corner and seven-time world champion Michael Schumacher steered into a wall 24 laps from the finish.
"It's clear we have a lot of work to do"
"It was a weekend to forget," said Ferrari chief Jean Todt. "Going home without points is a very bitter feeling, given that we had all we needed to succeed here."
Schumacher, who endured a miserable weekend, said: "I tucked in behind Jenson Button and unexpectedly I got some heavy understeer.
"Our main problem was keeping the tyres up to temperature, especially in the first part of the race and also because there were a few safety car periods.
"At first it was difficult to drive as after locking the wheels a few times the tyres were completely finished. It's clear we have a lot of work to do."
Kimi Raikkonen is confident his McLaren team have caught up with Renault despite finishing second behind Alonso.
Raikkonen had a final lap of one minute, 26.045 seconds, the fastest lap of the day, and finished 1.8 seconds behind the Spaniard.
"I am really pleased because we now have a package which is level with the Renaults which I think we demonstrated in Melbourne," he said.
"I was really pushing but in the final safety car period one of the Midland cars was between Fernando and I, which meant I was unable to get really close to have a go.
"It was an enjoyable race, and I can't wait for Imola."