Ahead of today's second session the air temperature is 29 degrees C, while the track temperature is 44 degrees.
While the Briton was 0.551s quicker than his teammate, third-placed Verstappen was 0.745s off the pace and Sebastian Vettel 0.849s.
The Silvers Arrows set their best times on the ultrasofts, as did Verstappen, while Vettel's was on the supersofts.
Having lost time earlier in the session with suspected exhaust issues, the McLarens made up for it late on with Alonso finishing the session 8th.
It was largely uneventful, and due to the fact it takes places much earlier than qualifying and the race pretty much unrepresentative.
That said, and admitting that this was the first practice session in a twenty-one race season, it was worrying to see both Saubers so far off the pace.
It is almost five minutes before the first car heads out, Magnussen, who lost track time earlier due to a sensor issue, in the Haas. He is followed by teammate Grosjean and Vettel.
Magnussen gets things underway with a 27.041, but this is soon beaten by Grosjean *26.412) and Vettel (26.141), the Dane and German on softs while the Frenchman is on supers.
Raikkonen (supers) posts 25.566, while Stroll goes third and Vandoorne fourth, the Belgian, like his teammate, quick to get to work in this session.
On the softs, like Vettel, Verstappen goes quickest (25.064), only to be leapfrogged by Bottas (24.719) who is also on the yellow-banded rubber. Alonso (softs) posts 25.823 to go fifth.
On the red-banded rubber Hamilton goes quickest (24.569), with Raikkonen improving to third (24.848) on the supers.
Bottas takes a trip through the gravel at T3 just moments after Ocon made a mistake at the same corner.
As Gasly complains about traffic, Hamilton is unhappy with the low sun.
Around twenty-five minutes into the session, after a flurry of activity, the Force Indias suddenly have the track to themselves, both are on the soft rubber.
The Pink Panthers are joined by Vettel, the German now running the ultras for the first time this weekend.
Vettel improves to third with a 24.451 but remains 0.066s off Hamilton's pace posted on the supers.
That said, the Briton now heads out on the purple-banded tyre as do Bottas and Raikkonen.
We are now about to see these four on the same rubber at the same time in the same conditions.
While Vettel looks set to improve, Raikkonen is on a flyer, the Finn crossing the line at 24.214.
However, Hamilton is quickest in S1, posting a PB in S2. At the line the Briton post 23.931 to re-take the top spot. Moments later teammate Bottas crosses the line at 24.159 to go second.
A brave but scrappy lap sees Hartley go ninth (25.925), two spots ahead of his Toro Rosso teammate.
By comparison, between the supers and ultras Hamilton found 0.454s while between the softs and ultras Bottas found 0.560s.
Sainz heads off through the gravel at T13.
On the ultras, Verstappen posts 24.058 to go second. Teammate Ricciardo is currently sixth and sticking with the softs.
Asked if he wants to do another lap, Alonso is in no doubt. "No, box," he replies.
Now on the ultras – as are most – Ricciardo posts a PB in S1, however a red flag causes the Australian to slow.
It appears that some wire, part of the timing system, has fallen on to the track.
"No...." moans Stroll, who is another driver who was on a hot lap when the red flag was waved, the Canadian is not happy.
The session resumes after a couple of minutes, Stroll and Hartley among the first back out.
"The red flag will make a slight difference to race preparations, with long runs interrupted," admits Pirelli. "But we're going again now, so the teams will still have plenty of data."
Magnussen improves to ninth (25.246) but remains a few places behind teammate Grosjean (24.648).
Everyone on the purple-banded rubber now.
The stewards reveal that they are to see Raikkonen regarding the earlier incident involving Bottas.
Having had his hot lap ruined by the red flag, Ricciardo hasn't reappeared. However, it is understood the team is making changes to his set-up.
Another off for Bottas, this time at T9.
"Default 34, default 34, urgent!" Alonso is warned.
Ricciardo is back on track, the Australian no doubt keen to pick up where he left off.
As Verstappen is told to "deactivate the warm button", Alonso runs wide as he continues to push to the limit and beyond.
With 16 minute remaining, Alonso is now the only driver not on track.
The Sauber pair are split by just one-thousandth of a second.
Rather than going for a low-fuel qualifying run, Ricciardo has opted to join the others in their race (long run) simulations.
With all 20 cars on track it is understandable that there are a few 'incidents', Gasly causing problems for Verstappen being one of them.
A late bit of cross-country for Ricciardo, the Australian running wide in the final moments of the session.
A late problem for Stroll also, the Canadian pulling to the side of the track with a suspected cooling issue.
As the drivers head to the grid to perform more practice starts, the final order is: Hamilton ahead of Verstappen, Bottas, Raikkonen, Vettel, Grosjean, Ricciardo, Alonso, Magnussen and Vandoorne.
Sainz is eleventh, ahead of Perez, Hulkenberg, Stroll, Ocon, Hartley, Gasly, Sirotkin, Ericsson and Leclerc.
Check out our Friday gallery from Melbourne, here.