Nico Rosberg says Mercedes' Baku F1 practice tyre plan hindered him

Rosberg spent time on the medium tyre early in second practice while Hamilton began with softs before both went for their fastest times on super-softs.

Hamilton ended the session with a 0.690-second margin over Rosberg.

The championship leader said it was Mercedes' policy to alternate which driver was tasked with evaluating the hardest of Pirelli's three compounds at each grand prix, but felt being on medium duty on the new Baku street track was a blow for him.

"Lewis was pretty quick today," Rosberg acknowledged.

"I had the disadvantage of having to run the medium tyre this afternoon, whereas Lewis was always on softer tyres so he could get up to speed quicker.

"That hindered me a little bit.

"One weekend it's that way, one weekend it's the other way. At a new track like this, it's a bit more penalising.

"But tomorrow I have plenty of time to work on one-lap speed and I'll get there."

Rosberg also had to sit out the last 20 minutes of second practice when his car came to a halt with an engine problem.

Mercedes is still investigating the cause, but Rosberg said it was a high-mileage unit for practice.

"It felt like an hour, sitting on the camping chair there it really felt a long time," he joked.

"Not ideal, but I still got a good run on high fuel so I still got to learn what I needed to learn. I didn't lose much.

"The engine was very old so even if there is a problem with it, it's not an issue at all.I'm not worried."

Mercedes' customer engine teams Williams and Force India were its closest rivals on the timesheets on Friday, with usual opposition Ferrari and Red Bull further down the top 10.

"It's a bit strange and difficult to understand where Ferrari and Red Bull are," said Rosberg.

"They're usually our biggest rivals and they seem to be a bit further back."