NicoRosbergShanghai2015_large.jpg[/timg

But his day was dampened after his right-rear tyre exploded as he headed to Blanchimont at high speed during the second session.

The German, who is due to become a father for the first time in the coming days, mercifully avoided contact with the barriers and his Mercedes, minus one of its Pirelli tyres, ground safely to a halt.

Rosberg is a very lucky boy.

Huge tyre failure, but plenty of run-off means he's ok. http://t.co/xcTgU7tSaI #bbcf1 pic.twitter.com/5m4k7gKmtf

— BBC Sport (@BBCSport) August 21, 2015

It was a harrowing moment for Rosberg, who left his cockpit before returning to the garage, The cause of the failure remains unclear and it will be of high concern both to Mercedes and Italian tyre manufacturer Pirelli.

Up until that point, Rosberg had dominated Friday’s practice. His quickest lap of one minute 49.385 seconds was three tenths faster than Hamilton who, as in the morning session, had to settle for second behind his team-mate.

Red Bull were best of the rest with Daniel Ricciardo, who benefited from Rosberg’s collision with Hamilton to claim victory here last year, in third. The Australian was 0.751sec down on Rosberg’s best lap. His team-mate Daniil Kvyat ended the session in fourth.

Ferrari are celebrating their 900th grand prix this weekend and Kimi Raikkonen, who is to remain with the Italian team next season, was fifth fastest finishing ahead of Sebastian Vettel in both sessions.

Rosberg’s high-speed tyre failure brought the second practice session into life. Shortly after the drivers returned to the track it was the Sauber of Marcus Ericsson who was then involved in a heavy shunt.

The Swedish driver lost control of his Sauber and slammed into the tyre wall. He sustained damage to both the front and rear of his car, but emerged from the shunt unscathed.

It led to a second red flag of the session and a third of an incident-hit day in the idyllic surroundings of Spa-Francorchamps. Earlier, Pastor Maldonado, the error-prone Venezuelan, thumped into the wall at Malmedy.

He was unharmed in the incident and following a sterling repair job by his Lotus mechanics, emerged back on track midway through the second session.

McLaren have become accustomed to propping up the rear this season and there will be little respite for the beleaguered team in Spa.

Indeed Fernando Alonso and Jenson Button have been hit with a combined 55-place grid penalty for Sunday’s race following a raft of changes to their respective Honda power units.

It means they will start at the back of the pack, and to make matters worse the new-spec Honda engine which they have brought with them to Spa has failed to have the desired effect at a circuit which relies heavily on power.

Button and Alonso ended the second session 17th and 18th respectively, quicker only than the Manor pair of Will Stevens and Roberto Merhi.

Elsewhere, Nico Hulkenberg was sixth in his Force India, with Romain Grosjean, whose Lotus ground to a stuttering halt in the closing stages, in seventh. Ericsson was eighth quickest ahead of his team-mate Felipe Nasr, celebrating his 23rd birthday. Vettel, winner last time out at the Hungarian Grand Prix, rounded out the top 10.