Stricker, playing for only the fifth time this year, holed out from the 10th fairway for eagle and made a 60-foot birdie putt across the fourth green for a 5-under 66 that gave him a share of the lead with MacKenzie, who had a 67.
Spieth is just happy to be joining them. He opened with a 76 and was in danger of missing the cut, especially when the wind began to pick up just as he was starting his second round on the Copperhead Course at Innisbrook.
And then he hooked his tee shot on the par-5 opening hole into a bush, had to take a penalty shot and made bogey on the easiest hole on the course.
''I'm walking off that green going, 'Oh, boy. We can either somehow flip this one around today or ... I don't want that to be the key of me not being able to be here for the weekend.' I thought it was really strong what we did after that,'' he said.
Nearly five hours later, after he nearly holed a bunker shot on the 17th to save par, Spieth exhaled on the 18th tee and said with a smile, ''This was grinding today. I've got some good stuff coming on the weekend.''
He wound up with a 68 and was at 2-over 144 to make the cut by one shot. That's all he was thinking about until he chipped in from behind the green on the 15th for a birdie, and his tee shot on the 16th narrowly cleared the water.
It was hard work, and there is plenty left.
More than just trying to make up seven shots on the weekend, he had 42 players in front of him.
Stricker began to cut back on his schedule a few years ago, and he had back surgery at the end of 2014 that limited his playing even more. But the strength is starting to return to the 49-year-old with the pure putting stroke, and he has looked solid for two days.
Stricker was tied for the lead early on Thursday until three straight bogeys late in his round. This time, he took the eagle and keep running, adding a short birdie putt on the par-5 14th and a 10-foot birdie on the 16th hole to catch MacKenzie.
''There are times I escaped with a few good breaks,'' Stricker said. ''Holing out on 10, you don't expect to do that. And that putt at No. 4 was going pretty quick, and that ended up going in. So some things evidently went my way. I'm starting to play a little better. Definitely putting better. And slowly, things are coming together.''
The large group at 3-under 139 included Justin Thomas, who hit a sharp slice to escape the trees on his first hole of the day (No. 10) and turned potential bogey into birdie on his way to a 67. Also at 139 were Augusta, Georgia, native Scott Brown (69), who has yet to play the Masters; past champion Retief Goosen and Charles Howell III, another Augusta native who had a 72.
Only eight shots separated the top and bottom of the leaderboard, leaving the weekend wide open.
That includes Spieth, the defending champion, whose first goal was get to Saturday. It wasn't easy, but he settled into his round with a 6-iron over the water to 5 feet on the third hole. He used the blade of his sand wedge to hole a birdie putt from the collar the par-5 fifth - the first time he has used that shot in competition - and putted one from off the green on No. 7 for another birdie.
He lost an easy birdie opportunity on the par-5 11th when he barely got out of a greenside bunker and was in deep rough. But he holed a 4-foot par putt that could have sent his momentum in the other direction, and despite missed birdie chances on the next three holes, the chip-in on the 15th was key.
''Today it was all about the cut,'' he said. ''All of a sudden I'm over the green on 15, kind of sitting down in the bluegrass rough just trying to hope to chip that one to tap-in range. ... Then all in all, we get finished and we're back in the tournament.''
Among those missing the cut were Keegan Bradley, who followed his 67 with a 79. It was more critical to Harris English and Webb Simpson, who were outside the top 66 in the world and will not qualify for the Dell Match Play in two weeks.