It's not ideal that Duran gave up the run, but not even the most dominant reliever carries an ERA of 0.00 through an entire season. Bottom line, the pitching and defense held the other team to 3 runs; so an offense with aspirations toward making some noise in the post-season ought to win such a game, way more often than not.
Don't blame a "bullpen leak", don't blame the umpires. Don't blame SWR's slightly short but very good outing, nor Steven Okert; between the two of them, they achieved 2 runs in 6 innings, otherwise a Quality Start except it took two of the to do it, which is then turned over to the bullpen in normal circumstances.
Blame the offense. Except for that blip during the winning streak against weaker overall opposition, they've been the problem this season. Every team tries to whomp mistake pitches, and every team tends to feast on a starter or a member of a bullpen who is having a bad day. But the good teams are able to switch gears and find-a-way against the typically good major league pitcher having a typically good outing.