Nearly three hours were lost due to inclement weather on day one and 44 players had to return to complete their first round at a Masters that had been delayed by seven months due to the coronavirus pandemic.
Casey was not one of those, having carded a bogey free round of 65 before darkness descended at Augusta National Golf Club to open up a two shot lead.
Frittelli had nine holes to complete in his first round and having hit a ragged tee shot at the first with his final act before the overnight suspension, he recovered beautifully, putting his second to 15 feet for a birdie.
Another poor tee shot came at the second but he got up and down beautifully to take advantage of the par five, before putting his opener on the par three sixth to nine feet and joining the lead.
Johnson had four shots to make up in his nine holes in the morning to join Casey and he made serene progress through the field.
A tee shot to 11 feet at the famous 12th set up a birdie and he made the most of the par five 11th from 20 feet before almost finding the cup from the tee at the 16th.
A stunning shot using the contours at the last then set up another gain from inside ten feet and Johnson shared the lead.
Thomas had been the dangerman overnight after a flying start to his round but he made just a single birdie upon the resumption after a lovely up-and-down from over the back of the 15th.
Im had 11 holes to complete and he made a flying start with a hat-trick of birdies from the eighth.
He made another gain on the 13th but gave it back after finding water on the 15th, before holing a 20 footer on the next.
Rose was three under as he completed the ninth on Thursday evening and he put a tee shot to ten feet at the 12th and made a two putt birdie on the par five next to edge up the leaderboard.
Smith was the morning's big mover, picking up birdies on the second, third, fourth, eighth and ninth.