Brad Penny just left a game that quickly unraveled. Through the first two outs of the fifth inning, he was shutting out the Rangers and pitching as well as he had at any point this year. Then, Julio Lugo undermined his cause, and Penny’s outing went from commanding to retreating in the span of three outs.

Lugo’s inability to field a grounder in the fifth allowed the first Rangers run to score, then sustained the inning to allow a three-run homer by Ian Kinsler. Then, with two outs and a runner on first in the sixth, Lugo failed to come up with a grounder up the middle and to his left, his dive ultimately proving inadequate. Again, this was a ball that a shortstop with average range would have turned into an out; Lugo did not, and the ball dribbled into center for a single.

And so, instead of another concluded inning, Penny had a two-out situation with runners on first and second. That turned into another run when Chris Davis jumped on a fastball and slammed it to deep right field, where it bounced into the stands for a run-scoring, ground-rule double. That signaled the end of Penny’s night. The right-hander was yanked trailing 5-0.

Penny’s line will suggest that he logged 5.2 innings giving up five runs on seven hits and two walks while striking out five. But that yield could have been far less, perhaps as little as one run. And so Brad Penny — a free agent at the end of the year, for whom every earned run will likely cost him money — had his ERA go up from 5.63 to 5.85, on a night when that mark could have easily drifted downward.

Rangers starter Kevin Millwood has endured no such betrayals. He has contained the Sox through six innings, scattering five hits, and he leads, 5-0.

Worth noting: many are crediting the emergence of the Rangers as a first-place team in the A.L. West with significant defensive improvement, brought in part by putting Elvis Andrus at shortstop and moving Michael Young to third. The Rangers currently rank sixth in the majors with a 70.5 percent defensive efficiency. The Sox, as mentioned earlier, have a 67.3 percent mark that is 27th in the majors, and tonight, the difference in the game has been defined by that gap.