Commentary: The Mariners got a huge boost with Luis Castillo. Here’s why they need to do more.

On a night the Mariners flailed in vain against Justin Verlander, they took a huge swing … and connected.

It was midway through another disheartening loss to Houston on Friday when news filtered out: The Mariners had finalized a deal for Cincinnati’s Luis Castillo, widely considered to be the best pitcher available on the market, as Tuesday’s MLB trade deadline approaches.

It’s just the sort of bold play the Mariners needed to make to end their playoff drought – and set themselves up to make a deep run if they finally, really and truly, get there.

Yes, there’s risk. There always is in deals such as these. The price tag was steep, which will alarm those Mariners fans with still-painful memories of, say, Jason Varitek and Derek Lowe for Heathcliff Slocumb in 1997.

They gave up their highest-rated prospect, shortstop Noelvi Marte, and another shortstop who many believe is on the verge of shooting past Marte on the list – 18-year-old Edwin Arroyo, who is tearing up Low -A Modesto. They also sent the Reds two promising pitchers in Levi Stoudt, who is at Double-A, and Andrew Moore, who is at Modesto. Marte, Arroyo and Stoudt are the first-, third- and fifth-rated prospects in the Seattle system by MLB.com.

But it’s foolhardy to let the fear of future breakouts by minor-leaguers in the low minors prevent you from going all-in – particularly when you’re staring at a 21-year playoff drought. That requires a different outlook and the sort of boldness that Mariners President of Baseball Operations Jerry Dipoto exhibited in getting a frontline pitcher such as Castillo, who has one more full season before being eligible for free agency.

It should be reassuring that the Mariners’ farm system is still stocked with numerous highly touted prospects who weren’t touched in this deal, topped by catcher Harry Ford and pitcher Emerson Hancock – not to mention outfielder Jarred Kelenic.

Whether not those players or others could be the foundation of another trade before Tuesday’s deadline remains to be seen. This package for Castillo would seem to take the Mariners out of contention for the biggest prize on the trade market, outfielder Juan Soto – unless Dipoto takes “all-in” to a new dimension.

There has been increasing recent speculation that the Angels are listening to offers for Shohei Ohtani, but I have a hard time imagining Angels owner Artie Moreno approving a trade of his most marketable player under any circumstances, and then doing so to a team in their division, and then doing a deal with Dipoto, who resigned in Anaheim seven years ago amid a power struggle with then-manager Mike Scioscia.

Those who have been watching the Mariners are screaming that what they need is a bat, not an arm. Well, they need both, and I would almost guarantee Dipoto is not done. In Castillo they get the sort of power arm (2.86 earned-run average in 14 starts, 90 strikeouts in 85 innings, 3.3 WAR) that will serve them well in a short series. It will also allow them to slow play the innings workload of rookie George Kirby to keep him fresh for the stretch drive and potentially the postseason.

If Soto is a no-go, as it appears, Dipoto will definitely need to augment their offense as his top priority. The Mariners have been winning a lot of close, low-scoring games, but that’s a risky formula for long-term success. They could be targeting the likes of Ian Happ, Brandon Drury, Jon Berti, perhaps Brian Reynolds or others – not to mention a backup catcher so they don’t run Cal Raleigh into the ground.

Dipoto jumped the market by getting DH/first baseman Carlos Santana on June 27, and the Mariners have soared ever since, excluding their five recent games with the Astros. They started 17-1 after acquiring Santana and through Friday’s loss at Houston stood 20-6 with him on the roster. It’s a reminder that relatively under-the-radar moves can nevertheless have a galvanizing effect on teams if the chemistry is right.

Last year, of course, the chemistry was all wrong when, on July 27, the day after a thrilling win over the Astros, the Mariners traded team leader Kendall Graveman to Houston for veteran reliever Joe Smith, a rental, and Abraham Toro. With a demoralized clubhouse, the Mariners lost eight of their next 11 games, which likely cost them the playoff spot that slipped away on the last day of the season.

The onus was on Dipoto this year to do something impactful to show the clubhouse, particularly the veterans (not to mention the fans), that they are serious about going all in this year. The Mariners have always said the prospects they’ve stockpiled through the years of their rebuild serve a dual purpose – to build up the big-league roster, of course, but also to be used as trade chips to finish off the team when it gets into a playoff chase.

That moment has arrived, and Dipoto took a strong first step Friday. The Mariners have to expect that their rivals will get better in the next few days; they had to least keep pace, if not do something that is a separator. These recent games against Houston show they are not yet on par with the Astros (and by extension, the Yankees). The arrival of Castillo helps close the gap – and they need to close it even further before Tuesday. That’s why I have referred to this as the most important trade deadline in Mariners history – or at least since 1995.

There has always been an unspoken (and sometimes spoken) covenant from Mariners management to fans that when the time came, it would use its resources (financial or otherwise) to enhance the team’s chances.

Keep in mind, with Houston likely unapproachable in the AL West standings, the next goal would be to wrap up the No. 1 wild-card spot and ensure that the first round of the playoffs is played at home – a huge advantage.

The Mariners can do that. They can also slip out of the top three and experience another agonizing playoff near-miss, just like last year (and several other years). There are no guarantees when it comes to a pennant race.

But this is shaping up as a year in which the Mariners’ playoff chances are beyond merely wishful thinking. They have a deep and talented pitching staff, and a budding 21-year superstar who can lift the offense. They have displayed a knack for finding a way to win, which sounds vague but is reflected in a 53-31 record in one-run games over the past two seasons.

All they need is a little boost. Or, even better, a big boost. And on Friday they got one. There should be more to come.