The three frontrunners of the 2020 marathon benefitted from an advantageous position in the running order for the 476km Wadi ad-Dawasir - Haradh stage, following their low-key finishes on Monday.
But whereas Peterhansel and Al-Attiyah took full advantage, clocking in first and second at nearly every waypoint, Sainz suffered a costly five-minute loss shortly after the 100-kilometre point.
And with Al-Attiyah just 15 seconds behind stage winner Peterhansel at the finish, the Toyota driver slashed Sainz's lead in the marathon down to less than a half a minute.
The gap between Sainz and third-placed Peterhansel, meanwhile, has been halved and now stands at 6m38s.
#405 South Racing - Can Am: Casey Currie, Sean Berriman