Rustand, 37, shot his 67 on the par-72 Meadow Course at Forest Highlands Golf Club to end the day at 5 under. He had six birdies in the round, including three straight from the 14th hole.
'I'm hitting the ball well and these courses set up well for me,' he said. 'I like to play the ball left-to-right and you can play that on every shot out here. Once I got over the nerves of it all, I was fine.'
A one-time professional -- he finished seventh at the 1999 Tucson Open on the PGA TOUR -- Rustand regained amateur standing in January following a three- year waiting period and is competing in his first USGA event.
'I got tired of doing this for a living,' he said. 'I just enjoy playing, period.'
Hybl, 25, had a 4-under 67 on the par-71 Canyon Course. He finished off the round with consecutive birdies at his last two holes to join Rustand.
'I feel really good about that round,' said Hybl, also playing in his first Mid-Amateur. 'This is a hard golf course and I think we played in some pretty tough conditions. There was some swirling wind and a little rain once in a while.
'I'm pleased with the round. I hit the ball pretty well and I putted the ball pretty well. All in all, just a solid round.'
Defending champion Kevin Marsh shares third place with two-time USA Walker Cup player Trip Kuehne after both shot 4-under 68 on the Meadow Course.
'The hardest part is playing with the expectations I have now,' said Marsh, who is attempting to become the second player ever to defend his Mid-Am title. 'I play my best when I just go out and see what happens. I got off to a hot start, and I'm happy with my 68, but I left three or four birdies out there.'
David Bartman had a 2-under 69 on the Canyon Course, while Joe Behl and Bill Williamson went 2-under 70 on the Meadow Course.