(CNN) -- All eyes were on triple world champion Sebastian Vettel during practice ahead of the Chinese Grand Prix, with the German back behind the wheel for the first time since ignoring team orders to clinch victory in Malaysia.
The Red Bull driver was left frustrated at the Shanghai International Circuit, struggling for pace as he registered the 10th quickest lap time.
World championship leader Vettel was one and a half seconds off the leading time set by Ferrari's Felipe Massa and insisted improvements were needed ahead of qualifying on Saturday.
"Today was a tricky day for us," the 25-year-old told the sport's official website. "I struggled a bit this afternoon and the gap to the guys at the top is a little bit bigger than I'd like.
"There are two or three things that we need to work on and then we should be in a better shape for tomorrow.
"I think we know what we need to do. It looks like the soft tyre is the one for qualifying, but it seems that we won't see that many stints on the soft tyre during the race."
Webber, who was upset by Vettel's decision to overtake him last month despite being instructed by Red Bull to hold position, performed better than his colleague, clocking the fifth fastest time of the day.
For Massa it continues a bright start to 2013 which has seen him outperform his double world champion teammate Fernando Alonso.
"Today, I immediately had a good feeling in the car," explained Brazil's Massa, who is four points ahead of Alonso in fifth position in the drivers' standings.
"I feel confident and hope that the whole weekend can keep moving in this direction."
Lotus' Kimi Raikkonen, winner of the season-opening Australian Grand Prix set the second fastest time.
The 2007 world champion was satisfied with the performance of his Renault car and is optimistic ahead of the weekend.
"If you look at the lap time it looks to have been a pretty okay day," said the Finn. "For sure, there are things we have to improve and you never know what will happen tomorrow, but it's a reasonable start to the weekend.
"We can definitely improve. We have some pace to come from the car in the usual areas with setup.
"My quick lap today could have been better, so there's some more pace to come even if we don't improve the car, but hopefully we do."