On a day when the Padres optioned pitcher Wade LeBlanc to Triple-A Tucson, they also purchased the contract of Spence, who had a 1.71 ERA in 35 appearances in Double-A with 42 strikeouts, 11 walks and 29 hits allowed in 47 1/3 innings.
Spence appeared in 45 games over parts of two seasons, throwing 71 innings before he earned his promotion.
Spence, selected in the ninth-round of the 2010 Draft out of Arizona State, is a native of Geelong, a port city located in Victoria, Australia.
Pat Murphy, the manager of the Padres' short-season affiliate in Eugene, Ore., coached Spence at Arizona State. Spence was 10-1 with a 2.37 ERA as a junior for the Sun Devils before being selected in the third round of the Draft in 2009 by the Angels.
But Spence, who has good command and leans more on his slider and changeup than his velocity, turned down the Angels' offer to return to Tempe. He didn't pitch as a senior at Arizona State due to a nerve issue in his elbow, which is likely why he slid to the Padres.
"We knew he was polished when we drafted him. He was one of the best pitches in the country as a junior," said Padres general manager Jed Hoyer. "We sent him right to San Antonio because we realized he was on a fast track."
Randy Smith, the Padres' director of player personnel, said Tuesday that Spence was a "finesse guy with good command."
"He has a good slider and a good changeup and a great feel for pitching," Smith said of Spence, who also has a very good pickoff move.
Spence was with San Antonio on Monday as the team played in Corpus Christi, Texas. He took a morning flight from Corpus Christi to Dallas and then another flight to Boston, where he arrived with a smile and little in the way of clothing.
"I packed a pair of jeans and a T-shirt [for Corpus Christi]," he said.
In order to make room for Spence on the 40-man roster, the Padres designated outfielder Luis Durango for assignment. The team also requested unconditional release waivers on infielder Jorge Cantu.