The Diamondbacks selected Nelson's contract from Triple-A Reno ahead of his scheduled start Monday in San Diego.
Nelson will be making his MLB debut Monday, with his performance against the Friars likely to dictate whether he sticks around with the Diamondbacks as a member of the six-man rotation. The 24-year-old owns an unremarkable 5.43 ERA over 136 innings on the season, but he's shown significant improvement since making some mechanical tweaks in late May that enabled him to sharpen his command. Over his final three months at Triple-A, Nelson turned in a 4.61 ERA, 1.34 WHIP and 85:31 K:BB across 95.2 innings.