The National Sports Collectors Convention arguably has never had a more exciting moment in its 39 years than what happened Friday in Cleveland.

Vintage Breaks, a company that offers collectors a chance to buy spots in unopened packs of vintage cards, charged $500 for spots in a 1955 Bowman pack.

On a stage, wired up to the crowd, owner Leighton Sheldon screamed when he saw the second-to-last card in the pack.

"My eyes bulged out of my head," Sheldon said.

What Sheldon saw was the most valuable card in the set: a Mickey Mantle, which appeared to be in pristine condition.

The new owner of a 1955 Mickey Mantle Bowman card, found in a vintage pack Friday at the National Sports Collectors Convention, has received an offer of $50,000 for it. Courtesy of Vintage Breaks

Some 375 miles east of Cleveland, Chris Rothe was finishing up his job as a third-generation bookbinder in Maryland when he decided to check the archived videos of the pack openings from earlier in the day. Rothe, who randomly got the 19th card that was to be opened in the pack, discovered that he was the proud new owner of the Mantle card.

"My friend told me my face went pale white when I saw it," Rothe said. "I was weak in the knees."

Rothe said he knew immediately that he would sell the card.

"I have the card in a 3 [on a 10 scale]," he said. "That's good enough. I'll use the money to get a [Roberto] Clemente rookie and maybe get a lower-graded Mantle rookie."

But the price Rothe expected to get for the card has risen significantly.

On Saturday morning, Sheldon returned to the convention and took the card to be graded by PSA, considered the industry's authority on the condition of cards. Three hours later, PSA returned with a grade of 9 out of 10 (a PSA 10 card is deemed to be in virtually perfect condition and gives the card its highest possible value).

It marked only the eighth time that PSA gave a 1955 Mantle Bowman card a 9 grade. Sheldon said he was told by PSA officials that it was the first time in more than two decades that they had graded that card a 9.

The last PSA 9 for the 1955 Mantle Bowman sold for $35,089. All day, Sheldon was working the show and the phones. By 7 p.m. ET Saturday, Sheldon had an offer for $50,000 for the card.

Rothe won't be the only one who will come away a big winner from a future sale. So, too, will Sheldon. His Vintage Breaks company, which has existed for a year, has never had such a high-profile pull. His greatest success to date was when a Michael Jordan rookie card was pulled from a pack of 1986 Fleer basketball. A collector paid $2,000 for the right to the unknown card before the pack was opened. Given its condition, the Jordan rookie was worth about $5,000.