The pair were ninth and fifth respectively with a round to go, but dropped back to joint 16th with rounds of 73 and 74.
What pleased the two stars was that they had had a chance to test their games in wind and rain, conditions expected to be repeated at Royal Lytham this coming week.
World number one and defending Scottish Open champion Donald said: "I'm leaving here with good feelings about where my game is.
"I did get much out of the round - a few lip-outs and a few bad bounces - but it was nice to play in a bit of wind and test out what I've been working on.
"You had to hit penetrating shots and it felt like I had pretty decent control. Certainly good enough to contend next week.
"I had three weeks rest before this and I'm ready to go. I'll even consider 18 holes each day (before the start on Thursday) if the weather is not horrendous."
Mickelson, who asked for a late invitation to try to find his game after a poor two months, had middle rounds of 64 and 65.
"I think it was a great week," said the 42-year-old, joint runner-up behind Darren Clarke at Sandwich last year after coming only 58th at Castle Stuart.
"To have two good rounds and then to play in some challenging conditions was a plus too.
"Players here got a lot out of the week, myself especially, and I feel a lot better than I did three days ago."
He was not even in the top 120 with his opening 73.
Padraig Harrington finished on the same 12 under par mark after a 71 that included an adventurous bogey six on the second.
His drive was found on the beach under what looked like an abandoned door.