Lewis Hamilton overcame further technical issues to set the fastest time of the day on Friday afternoon.
The world champion posted a 1:39.790 on a blisteringly hot afternoon in Malaysia that saw the track temperature surpass 60 degrees, a figure not seen in several years. As a result the usual gain in option tyre performance was a little less than usual as the heat made the circuit less grippy.
Before setting the headline time of the day on the medium compound tyres, Hamilton had missed the first 40 minutes of the session as the team fixed a problem with the inlet system on the power unit which had caused him to stop out on track, he was also still blighted by the telemetry issues that had hampered the team since the start of the day.
Ferrari on the charge
The very hot conditions also meant there was more mistakes out on track as Nico Rosberg and Sebastian Vettel made errors on their qualifying simulations resulting in lost time with Rosberg taking third behind Kimi Raikkonen and Vettel seventh.
It does appear, however, that Ferrari are in a position to at least keep Mercedes on their toes as the Scuderia have opted for more straight line speed while the Silver Arrows decided on greater downforce.
In the race in Australia, the two Prancing Horse's were able to match the Mercedes pace for periods of the 300 kilometres and should it stay dry, then an intriguing battle awaits.
Red Bull making progress in bid to catch Williams
There was also hope at Red Bull as Daniil Kvyat posted the fourth best time just over half a second slower than Hamilton's benchmark.
Issues continued to hit his team-mate Daniel Ricciardo, however, as an engine issue meant he was only running on five cylinders in his RB11. As a result, therefore, his 10th place in second practice seems a very good result.
Certainly it seems they could move clear of the midfield and look to challenge Williams who had another relatively quiet afternoon.
Valtteri Bottas led team-mate Felipe Massa as the pair ended fifth and sixth respectively in what was the closest session so far with eight tenths covering the top seven.
Teen Verstappen leads increasing midfield battle
Teenager Max Verstappen continued his solid first day of running at Sepang taking eighth quickest in the Toro Rosso leading Marcus Ericsson who also had a better day in the Sauber.
If Ricciardo and Red Bull are to move clear then it is one less team from what has become an even bigger midfield battle for the final points paying positions.
Sauber and Toro Rosso led but Lotus and Force India are all very much in the mix as well with just 1.4 seconds covering Verstappen in seventh to Jenson Button in 17th with an engine issue meaning Romain Grosjean was stranded in the pits for the final 30 minutes of the session and ended 18th.
McLaren still off the pace
McLaren have made progress but still seem the least likely of the five midfield teams to be challenging for points.
Fernando Alonso was a tenth clear of Button as the two Honda-powered MP4-30's brought up the midfield pack, their lack of speed could be down to running a lower engine mode as they completed just shy of 50 laps combined in the afternoon which was a good achievement given previous problems and the very hot conditions.
Stevens gives Manor something to cheer
At the back Manor Marussia continued to learn about their updated 2014 car with 18 laps on the board in the afternoon, however, the biggest achievement of the day was Will Stevens who set a time within the 107% needed to make the grid on Sunday. That means he at least should be given dispensation to race regardless of his time in qualifying providing those in front don't improve too much.
Unpredictable Sepang weekend awaits
Back at the front, however, and a very abnormal day with engine issues and mistakes on track meant we really have few clues as to just where the two Mercedes stand.
Lewis Hamilton may have been quickest but there is plenty more time in Nico Rosberg's pocket following his errors out on track. Add to that the fact Hamilton's car was running in lower engine modes to avoid more mechanical issues then we will only really find out where they stand on Saturday.
Behind it will be about whether Ferrari can maintain a weekend-long challenge to the Silver Arrows and if Williams and even Red Bull could be a part of it too.
Add to that the increasing likelihood of rain as the sessions start later in the day and you have the recipe for another very unpredictable weekend in Malaysia.