Grosjean was on course for a podium finish before being stopped by an engine issue, while Raikkonen overcame back problems to take an eventual third place.
Alan Permane, Lotus's trackside operations director, said the upswing in form - especially in qualifying - was encouraging now that F1 was back on high-downforce circuits.
"We had a nice qualifying this weekend, and we got it right for a change," Permane told AUTOSPORT.
"The car worked well and we had no issues at all.
"The rest of the races are on tracks that require similar downforce [to Singapore], and Pirelli are bringing sensible tyres rather than the hard combinations they did at the end of last year, so there is no reason why we cannot have a good finish."
"We would have been third and fourth without Grosjean's failure," he added.
"And honestly, if Kimi had had a proper weekend, they would both have been up there qualifying wise and had a decent race.
"I don't think anyone can race Fernando apart from Vettel and no one can race Vettel.
"He is out on his own. Totally, totally out on his own."
- Sports & Recreation
- Motor Racing
- Kimi Raikkonen
- Romain Grosjean
- Alan Permane
- Sebastian Vettel