The GRT Yamaha rider set the first 1m 26s lap of the weekend late in the session, to finish just over two-tenths clear of BMW's Loris Baz.

Title leader Toprak Razgatlioglu (Yamaha) and Friday pacesetter Jonathan Rea (Kawasaki) completed the top four.

Second on combined practice times courtesy of his FP2 lap, Rea was one of only five riders not to improve this morning.

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Rea, who had been half-a-second clear of nearest rival Razgatlioglu on Friday, picked up where he had left off in the early stages of the Saturday morning session.

Razgatlioglu then responded by moving to the top just before the midway stage of the 30-minutes, before Baz - who like fellow BMW rider Scott Redding has a new Kalex swingarm this weekend - then took over.

But Rea's 1m 27.016s Friday best stood firm until another surprise at the top in the form of Gerloff who - after several big sideways moments - put a clean lap together to set an uncatchable 1m 26.877s.

Rea's Kawasaki team-mate Alex Lowes was a close match for the six-time world champion in fifth, with Honda's Iker Lecuona suffering a scare when he ran wide on the exit of Redgate and took to the grass on his way to sixth. Team-mate Xavi Vierge was 16th after a small fall.

Title leader Alvaro Bautista, fifth on day one and predicting a defensive weekend against the likes of Rea and Razgatlioglu at arguably the worst track of the season for Ducati, made an early trip through the gravel at the Fogarty Esses on his way to seventh and top Ducati.

BMW's home star Scott Redding, the next best rider after Rea not to improve in FP3, then Ducati riders Philipp Oettl and Michael Ruben Rinaldi completed the top ten.

BSB title leader Tarran Mackenzie began his second day on a WorldSBK-spec R1 in 17th, with Peter Hickman 19th on the FHO Racing BMW.

The present UK heatwave means air temperatures are expected to top 30 degrees this afternoon.