Hughes' declining strikeout rate

Phil Hughes picked up his 14th win of the season yesterday, allowing three runs in six innings to beat the Royals. He didn't record a single strikeout in the start, which is something he had only done one other time in his career (a 1 2/3 inning effort against the Orioles in 2009). Hughes' strikeouts per 9 innings rate now sits at 7.35, which is the lowest it's been all season. Through May, it was around 9, and through June it was in the 8s. Yet, Hughes has maintained a similar rate of contact throughout the season. I've prepared a two-axis graph with one side showing cumulative K/9 and the other showing cumulative whiff rate (swings-and-misses per swings), centered around approximated league averages for both metrics. I find plotting whiff rate and strikeouts to be significant since swing and misses correlate well with strikeouts.

Other than his first two starts of the season (the second of which was a 10 strikeout, 1 hit performance against the A's), his whiff rate has not seen the decline that his strikeout rate has --- in fact, his whiff rate is currently slightly higher now than it was in the middle of May. So, to me, it appears that the recent dip is more of a typical regression than a decline in ability.

Gameday data is from MLBAM.