First, the numbers, as we sit in first place: 32-27 real record, with a 191/208 RS/RA that translates to an expected record of 27-32. So we're well ahead of our Pythagorean record.
But as I've pointed out before, we don't have to give any of those wins back. So the question becomes, what's our expected record the rest of the way? I'll give you a hint: it's not - or shouldn't be - 47-56 (which is what you'd extrapolate from our Pythag).
Why not? Because most of that RS/RA deficit was accumulated in the opening weeks of the season, when our offense was threatening to break all modern records for futility. Go back one month*, and we were at 89/115. Over the last 31 days, this team's RS/RA is 102/93, which gives you an expected record of 15-12. We've done better than that (probably in part due to weaker opposition - 12 of 27 games against Astros, Brewers, Cubs, & Royals), but my point is simply that we should expect this team to outperform its Pythagorean record all season long, because its April offense was an outlier, both relative to history and relative to its talent level. We're clearly a below average offense by talent, but not historically so. Due to good luck, we outperformed our Pythag when the offense was at its nadir; if we merely match our Pythag going forward, we can expect a solid record, well ahead of our season-long Pythag.
Additional points: Sunday's 3 runs ensured that our average RS over the past 3 weeks - that's 18 games - is above 4 (4.06 to be precise). Why does this matter? Because our team's xFIP is at 3.97, and has been hovering in the high 3s for awhile now. It may not be stabilized, exactly, but I feel pretty comfortable saying that, cascading injuries aside, our RA should stay below 4.00 going forward**. All of which is to say that, if we think the offense we've seen in the last 3 weeks is real and sustainable (and I'd argue that it is, roughly - a few guys are hitting over their heads, but we still have had Pedro and Tabata more than 50% below ML average), then this team should be able to stay above .500 for the rest of the year.
So what's my bottom line? Don't worry so much about our Run Differential and Pythagorean record, because they are largely artifacts of the opening month, but we've weathered that month, and have no real reason to expect it to recur. This team has been outscoring its opponents for a month now, and will most likely score roughly as many runs the rest of the year as it allows. Enjoy it.
* an arbitrary endpoint chosen not for how we've played, but simply because it's one month
**not only do we have pretty good options if one of the current starters gets hurt, but we also will gain in the battle between ERA and DIPS if/when Correia departs the rotation - he's due for about 2/3 run of regression, but if we replace him with a true-talent 4.30 SP, we'd have the same team ERA going forward but an xFIP that drops by over 1/10 of a run