The threesome sits at 9-under-par 133 through 36 holes, one stroke better than three other golfers, including defending champion and overnight leader David Toms, who backed up an opening-round 64 with a 70 on Friday.
Two strokes back at 7-under is another large group of six players, including young Charles Howell III, who carded a day-low 65.
While Riley and Kaye each recorded their 67s in the relative calm of early afternoon, Mattiace finished his round as winds began whipping through the Williamsburg area of Virginia later in the day.
His round began on a down note with a bogey-five at the par-4 1st, but the Jacksonville, Fla. resident turned it around with six unanswered birdies over the remainder of the day.
Four of those birdies came in a seven-hole stretch between the third and the ninth.
'I think when you are playing well, you want to let the flow go,' explained Mattiace.
'You want to let your momentum and your positive thoughts and your confidence take you to how ever many under you can shoot. I did that.'
In his seventh full season on the PGA Tour, Mattiace is still searching for his first win. While he has finished second on two occasions ' in 96 and 99 ' he has only recorded one top-10 finish this season at the Shell Houston Open in April.
Likewise with Mattiace, Toms also was in the top-10 at that particular event in Texas.
Since, however, Toms has been brilliant.
He won two weeks later at the Compaq Classic and then changed his life several months after that at the PGA Championship, where he claimed the Wannamaker Trophy on the 72nd hole.
Friday, though, he could do no better than 70 after turning everyones heads with his opening 64.
Riley and Kayes rounds were also head-turning.
They each shot 67 to end in joint first, but they came in decidedly different fashions.
Kayes score was composed of a mere four unanswered birdies, while Rileys day consisted of two eagles, four birdies, two bogies and a double-bogey.
In the end, both rounds equaled 67.
Just two back at 7-under, former NCAA champion Howell followed Kayes lead, producing a round of six birdies against no birdies for 65.
The 22-year-old sits two strokes better than another youngster in his first year as a professional, Bryce Molder.
Molder, also 22, shot a 71 to get to 5-under for the event.
Unfortunately, however, for the youngest player in the field, the week was not met with great success.
Competing in just his first event as a professional, 17-year-old Ty Tryon carded a 72 on Friday to end at 6-over-par 148.
He missed the midway cut, which came at 1-under 141.
Click Here for Full-Field Scores from the Michelob Championship at Kingsmill.