Sepang - Disappointed Mercedes team principal Toto Wolff described his team's woeful performance in practice for the Malaysian Grand Prix as "the worst Friday I can remember".
Wolff did not pull his punches after championship leader Lewis Hamilton and Valtteri Bottas could manage only sixth and seventh fastest respectively in both of Friday's practice runs.
"Whether it was in the wet, the dry, long runs or single lap, we lacked pace today," team principal Wolff told a press conference. "We only have 12 hours to get it right."
To make matters worse, Sebastian Vettel, who lies 28 points behind Hamilton in the race for the drivers' title, smashed the all-time Sepang lap record in his Ferrari, lapping more than 1.4 seconds quicker than the Mercedes.
"The lap time is reality. The lap time showed we are not quick enough. It is one of the worst Fridays I can remember," said Wolff.
Vettel clocked 1min 31.261sec around the 5.543-kilometre circuit to smash the old record of 1:32.50 set by Fernando Alonso in 2005.
Vettel's Ferrari team-mate Kimi Raikkonen was second quickest, six-tenths of a second adrift.
The Red Bulls of Daniel Ricciardo and Max Verstappen came next and even the McLaren of Alonso, which has been poorly paced all season, was fifth in the afternoon after being third fastest in the wet first session.
Hamilton sat in the garage for most of the morning as the rain teemed down.
And the three-time world champion was on just his 10th lap of the afternoon when he took too much speed into turn eight, resulting in a sideways excursion into the gravel.
"It's been a very difficult day," said Hamilton.
"I've been struggling with the car, so we have to review and try to understand where we have gone wrong with the balance.
"We're hoping that we're able to find our bearings overnight and regroup for tomorrow."
Bottas was optimistic the team could have a better Saturday.
"We're definitely lacking some performance, it seems like Ferrari and Red Bull are very strong," said the Finn.
"So we have some work to do if we want to be on the front row tomorrow. The key area we are going to need to focus on tonight will be getting the maximum out of the tyres over one lap."
The morning practice was shortened by rain and in the afternoon, when the cars could run on slick tyres, the session ended 20 minutes from the end when Romain Grosjean hit a loose drain cover.
The Frenchman's rear right tyre was ripped off at turn nine, throwing his Haas into the barriers at high speed and bringing out the red flag.