CINCINNATI -- With their 4-2 defeat on Wednesday, the Padres’ once-promising road trip ended with a dud. Consecutive losses put them right back where they started it -- eight games below .500.

For six innings on Wednesday at Great American Ball Park, the San Diego offense was mostly lifeless against Reds right-hander Luis Castillo. Francisco Mejía went deep in the seventh, but it wasn't enough. Five relievers combined to allow four runs on 10 hits and three walks.

• Box score

Here are four noteworthy talking points from the Padres’ three-game set in Cincinnati:

Bullpen day isn’t working
Remove the games in which the Padres used an opener or received a shorter-than-expected outing from their starter. That leaves four times the Padres have planned for a bullpen day this year.

They’ve lost all four, allowing 26 runs.

For the most part, those bullpen days have been the product of the youngest rotation in baseball. The Padres have made a concerted effort to give their starters extra rest, and it’s left them with gaps to fill. On Wednesday, for instance, Chris Paddack could’ve started on normal rest, but the club opted to push his start back -- as they’ve done all season.

“We did this to give Chris another day of rest,” said Padres manager Andy Green. “It wasn’t because of some strategic way we thought it was better not to throw Chris Paddack against the Cincinnati Reds. We didn’t set out to do this. Now, you still go out there with the attitude that you can win the game with this group of guys. I liked those guys in every situation they were in today.”

The Padres’ relief corps was mostly solid. Luis Perdomo was particularly sharp over three innings of one-run ball. Meanwhile, Matt Strahm and Craig Stammen pitched two scoreless innings apiece. But after Strahm was done, Eric Yardley loaded the bases on two hits and a walk in the third. With the bags full, Green called for Trey Wingenter, who walked in two runs.

Bullpen days might soon be extinct in San Diego. The Padres want to take the reins off their young starters next season, and they won’t be so rigid in finding extra off-days. Plus, it’s a goal of the front office to reinforce the rotation this winter. That means the Triple-A pitching depth should be much, much better.

Mejia is going to take his hacks
Castillo made Mejia look foolish on a three-pitch strikeout in the top of the second inning. That comes with the territory for Mejia -- who has a violent swing and a penchant for chasing out of the zone.

The Padres think his aggressiveness is worth the tradeoff. Four innings later, Mejia teed off on a letter-high fastball from Reds reliever Lucas Sims for his 11th career home run. Four of those have come in Cincinnati.

Mejia has been one of the sport’s hottest second-half hitters, slashing .333/.379/.573 since the break. That success might be a direct result of the changes in his approach.

When Mejia arrived at the Trade Deadline last season, the Padres worked extensively to hone his pitch selection. He struggled to make those adjustments. This year, when they sent Mejia to the Minors, they told him to do what he does best: swing away. It’s working.

Would the Padres like to see Mejia chase fewer pitches outside the strike zone? Of course. But going forward, they might be more subtle in the changes they ask him to make.

The outfield defense could be good -- but isn’t
All three Padres outfielders misplayed a ball into extra bases on Wednesday.

In the third, Josh Naylor dropped a routine liner on Yardley’s first pitch, sparking the Reds’ rally. In the fifth, Wil Myers misplayed a José Iglesias single into an extra two bases. In the seventh, Hunter Renfroe made an ill-advised dive on a Freddy Galvis liner, which became a double.

Presumably, Renfroe gets a pass, given the strides he’s made on defense this season. He entered play Wednesday leading all outfielders with 24 defensive runs saved.

But there are question marks surrounding Myers as a center fielder and Naylor as an outfielder in the first place.

The Padres remain optimistic that Naylor, a converted first baseman, is simply learning the nuances of his new position. Despite the occasional gaffe, Naylor’s defense has exceeded some expectations, and Green didn’t seem too concerned with Wednesday’s error.

“He was where he needed to be to catch the baseball, and he just didn’t catch it,” Green said. “You’ll see that from time to time across baseball. He takes it very personal and works hard.”

As for Myers, time is running out on his center-field prospects. The Padres still hope Franchy Cordero can be a lefty-hitting force. That wouldn’t leave much playing time in center for Myers -- or, seemingly at all, against right-handed pitching.

What might have been…
Here are the three lines for the Reds’ starting pitchers this week:

Trevor Bauer: 7 IP, 5 H, 3 R, 2 ER, BB, 11 Ks

Sonny Gray: 6 IP, 4 H, R, 3 BBs, 10 Ks

Castillo: 6 IP, 5 H, R, 0 BB, 4 Ks

That’s a 1.89 ERA and 25 strikeouts in three starts.

“They ran three really good starters out at us,” Green said.

The Padres could’ve had all three.

It’s unclear just how far trade talks ever progressed regarding Bauer and Gray. But San Diego had legitimate interest in both, according to sources.

Meanwhile, the Padres actually landed Castillo at the 2016 Trade Deadline -- in the same deal that netted them Naylor. But when Colin Rea went down with an elbow injury in his first start for Miami, the two clubs re-worked that trade, sending Castillo back to the Marlins. Later that season, Padres general manager A.J. Preller would be suspended for his failure to disclose medical information in a different trade.

Three years later, starting pitching remains at the forefront of Preller’s wishlist.