A tale of two players:
First consider their performances,
Player 1: 4.91 K/9, 2.98 BB/9, 56.2% GB, 1.38 HR/9, 5.02 FIP
Player 2: 5.27 K/9, 3.21 BB/9, 52.6% GB, 0.60 HR/9, 4.00 FIP
Pretty similar skill-sets, huh? Player 2 seems to have pitched better this season, but given better HR suppression, Player 1 could close the gap.
Pitcher's don't pitch in a vacuum, however. Much of the results on the field has to do with the defense behind a pitcher.
Player 1's Team: 18.1 Infield UZR + 14.5 Outfield UZR = 32.6 UZR
Player 2's Team: -21.8 Infield UZR + -14.5 Outfield UZR= -36.3 UZR
Their respective team's fielding prowess is reflected in their ERAs...
Player 1: 4.21 ERA
Player 2: 4.67 ERA
...and in the stories written about them.
Since pitching horribly in April/May with a strikeout-rate hovering around 1.5 K/9, Pelfrey has posted a 6.37 K/9, 2.99 BB/9 (May 23 to present). In that time span, his ERA has risen. Step back?