The benchmark from the reigning world champion is a 1m54.938s, 0.6s ahead of Piastri.
He sets a 1m55.549s to go clear of Verstappen - 0.5s between those two.
Verstappen, Gasly, Piastri, Hamilton, Norris, Ocon, Sainz, Leclerc, Russell and Perez.
A 1m56.003s for Verstappen, 2.0s ahead of teammate Perez in fourth. The times will only get quicker with no rain currently.
A 1m57.411s for Piastri, 1.3s ahead of Hulkenberg. Norris is 1.4s off in third.
Expect the times to tumble if conditions remain stable.
"Rain expected in just over two minutes," McLaren tell him.
Will this be the best of the conditions? The two Mercedes drivers have just taken to the circuit.
Only Hamilton and Russell are still in the pit lane. With more rain on the way, is that a risky move?
A number of drivers take to the track on the intermediates. More rain expected in eight minutes, say McLaren.
There hasn't been any rain for the last 15-20 minutes with conditions slowly improving. More, heavier, rain is forecast for this evening so getting qualifying done and dusted will be important.
Stroll crashed in FP3 and Aston Martin are still working on his car. It will be tight as to whether he will get out for qualifying at 3pm BST.
25 minutes until lights out at Spa! The F2 race has been postponed due to heavy rain - but since then, the rain has eased up considerably.
Heavier rain is forecast later in the day.
Verstappen fastest ahead of Piastri, Gasly, Norris and Ocon.
Two minutes on the clock and FP3 is back underway. This gives everyone a chance to do an out and in-lap.
A reminder of the top 10: Verstappen, Piastri, Gasly, Norris, Ocon, Leclerc, Stroll, Bottas, Hamilton and Perez.
No sign of conditions improving here.
Conditions are deteriorating so the FIA have put out a red flag.
Heavy rain at Spa so no cars are out on teack with 30 minutes on the clock.
FP3 is back underway...
Verstappen, Piastri, Gasly, Norris, Ocon, Leclerc, Stroll, Bottas, Hamilton and Perez.
Stroll has crashed.
Verstappen, Piastri, Gasly, Norris, Ocon, Leclerc, Bottas, Hamilton, Perez and Albon.
Piastri is told: "Expect this heavier rain to last for 10 minutes."
Verstappen remains top of the pile with a 2m01.565s, 1.4s ahead of Piastri.