Using all teams from 2010-14, the relationship between OPS differential and winning pct is
Pct = .5 + 1.3246*OPSDIFF
That estimates the Rangers to have a .515 pct (much lower than their actual of .644 thru yesterday). They are .129 above this projection (one big factor is they are 17-4 in 1-run games).
But their differential is much bigger in High Leverage situations than otherwise. The two tables below show the stats for the hitters and pitchers
So what are their OPS differentials in each case?
Using the same years mentioned above, here is the equation when breaking things down by leverage
Pct = .5 + .306*LOW +.420*MED + .564*HIGH
Estimating the Rangers pct here would be
Pct = .5 + .306*(-.050) + .420*(.034) + .564*(.109) = .560
That explains about 35% of the difference between their actual pct of .644 and the .515 predicted by just using overall OPS differential (or at least makes it 35% smaller). So what else might explain their performance?
The Rangers do lead the league in turning DPs with 94. The next highest total is 79. The league average is 66. So the extra 28 DPs probably helps, too.
They allow a .323 OBP while the league average is .321. So they are probably not getting too many more guys on base and should have about an average number of DP opportunities.
I am not seeing anything else that big that jumps out that would account for their high winning pct. They do take the extra base 43% of the time vs. 40% for the league average (that is, a runner advances more than one base on a single and more that two on a double). They are tied for 3rd in the league. The Indians lead with 49%. But the Rangers also lead with outs on base. So it seems like base running is not helping them too much.
They have played 38 games (a bit more than half) against the worst 6 teams in the league in taking the extra base. That might help a bit.
They do lead the league in bases taken on fly balls, wild pitches, passed balls and balks. They have 85 and the league average is 70. Seems small.
Getting back to their record of 17-4 in 1-run games, you might think it would be a result of their bullpen. But their bullpen has an ERA of 4.71, the highest in the league. Their bullpen has the 2nd highest OPS in the league at .792. The Twins have .806. The Rangers bullpen does lead the league in GDPs with 29.
Their entire staff also leads the league in GDPs in High Leverage Situations with 39. Seattle is 2nd with 31. The MLB average is 23. So those extra 16 DPs in key situations might help.
Their batters have hit into 29 DPs in High Leverage situations. Their net gain of 10 DPs is tied for 3rd in the league.