The Pittsburgh Pirates just wrapped up a series against the Arizona Diamondbacks, and if you only looked at the scoreboard, you might wonder how they pulled off a series win while scoring just five runs total. The answer? Dominant starting pitching.

After a rough 9-0 loss in the series opener on Tuesday, the Pirates bounced back in a big way. Wednesday night featured a tense 1-0 pitchers' duel, and Thursday's rubber match ended with a 4-2 victory. It wasn't pretty at the plate, but it was a masterclass in mound work.

When you need to stop a losing streak, there's no one better to hand the ball to than your top arms. On Wednesday, reigning Cy Young winner Paul Skenes delivered one of the finest outings of his career. He worked eight innings for the fourth time, holding Arizona to just two hits while striking out the side to close his outing. Skenes retired the first 14 batters he faced and the final 10 in a row, with only a pair of infield singles breaking up perfection.

On Thursday, Mitch Keller showed why he's become such a reliable force. After a shaky start—two runs allowed in the first two innings—the right-hander settled in beautifully. He retired nine consecutive batters before exiting in the seventh, finishing with six innings of two-run ball. It was his sixth quality start in eight outings this season.

Together, Skenes (2.36 ERA, eighth in the National League) and Keller (2.87 ERA, 16th in the NL) are carrying the rotation. Their combined 9-3 record is a huge reason the Pirates are off to a strong start.

But even with the series win, there were a couple of red flags that popped up over the three games—issues that could become bigger problems if not addressed.