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Nationals pitcher Stephen Strasburg struck out 14 batters in his major league debut last June. ((Greg Fiume/Getty Images))

Nationals pitcher Stephen Strasburg has thrown off a bullpen mound as part of his recovery from Tommy John surgery.

Washington manager Jim Riggleman says Strasburg was expected to throw at about 50 per cent Monday in Viera, Fla. Strasburg had been throwing off flat ground.

The overall No. 1 pick from the 2009 draft seemed excited about his return. He posted on Twitter: "First bullpen in the books. Felt great! Hopefully time will speed up now!"

The 22-year-old pitching phenom had ligament replacement surgery on his right elbow Sept. 3. It is expected to take 12 to 18 months for him to return to the majors.

Strasburg struck out 14 in his big league debut last June and went 5-3 with a 2.91 earned-run average in 12 starts.