Even if any doubts that Casey Stoner could no longer run the pace of the best in the world lingered after his public outings in 2016, the Australian comprehensively shattered them on Monday at Sepang.

Despite his status as a test rider since retiring at the tail end of 2012, Stoner displayed all of the explosive speed in Malaysia that carried him to 38 premier class wins as he posted the fastest time of the day.

Other riders found it difficult to comprehend his pace while acting as a test rider. "I saw his time and I'm not sure why he's not racing," said Maverick Vi?ales, while old foe Valentino Rossi joked, "It's very good that he don't race!"

Stoner was present at Sepang at the end of last week, but even then his on-track time was disrupted by bad weather. On Monday the two-time world champion posted an early time of 1m 59.680s, 0.117s quicker than second fastest Andrea Dovizioso. He will test again on Wednesday.

Such was Stoner's pace, his best time was a full quarter of a second quicker than the fastest dry lap time set at this circuit during the 2016 grand prix weekend, surely sufficient evidence that he still possesses the ability to regularly challenge for race wins if he ever sought a return to race occasionally.

The Australian didn't speak to the media after Monday's on-track action, but Ducati provided an official press release, complete with Stoner's comments.

"Today was positive and the best thing about it was that we got a lot of dry track time," it read. "It's been hanging in the balance really with the weather because the track takes so long to dry and if it rains at all within twelve hours, you're going to get very little track time.

"It's great that we got out there straightaway this morning and started putting in some good laps, reconfirming what we felt earlier in the week. We got a lot of comparisons done today so it was really good to get a feeling and direction with the bike.

"We still have a lot more work to do, it was disappointing that it rained but hopefully on Wednesday when we come back on track we can pick up where we left off and move this bike further forward, especially in the chassis area."

Stoner's performance was in contrast to the early struggles of Ducati's Jorge Lorenzo, who ended the first day of testing a distant 17th - 1.669s off the test rider's pace.

While his recent competitiveness comes as little surprise, Stoner's public testing outings with Ducati have always been worthy of note.

A year ago, he placed ninth overall at the official Sepang test, with the fifth fastest time on the final day. In a summer outing at a test which preceded the Austrian Grand Prix, he was third fastest at the Red Bull Ring.