Blake, who titled at the event in 2002, rallied for 4-6, 6-2, 6-2 victory, posting his second win of the season with a strong third set. The 32-year-old improved to 16-7 in his career in Washington.
Also Monday, French qualifier Florent Serra needed three sets but defeated American Brian Baker 4-6, 6-3, 6-4. Baker managed to convert just three of his 16 break point opportunities.
The Citi Open's main draw began, with Argentine Leonardo Mayer's 7-6 (7-5), 7-6 (10-8) decision over Spaniard Guillermo Garcia-Lopez in a 1 hour, 58-minute contest.