While the two young prospects have been OK at times, they have not reached expectations in a rotation that is heavily counting on them for the rest of the season.

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One is a 27-year-old southpaw whose fastball can hit 99 mph.

The other is a 23-year-old right-hander who can throw 95.

One is a Canadian-born fourth-round draft pick who began the year in the minors.

The other is a second-rounder who grew up in SoCal and started the Mariners’ fourth game of the season.

James Paxton and Taijuan Walker are hardly polar opposites, but there are distinct differences in their styles and career paths. Right now, however, there is one glaring commonality the two young pitchers share.

They need to step up their games ASAP.

It wasn’t long ago that this duo was part of Seattle’s “Big 3” pitching prospects, with the third being injury-plagued Danny Hultzen. The label was unfair given the uncertainty of player development in baseball, but the pair’s natural talent justified the excitement.

And while the results over the past couple of years have not been disastrous, they haven’t been commensurate with expectations. The thought was that if Paxton and Walker did what their capabilities suggested they could do for the Mariners, all would be right. Instead, they’ve just been all right.

“These are guys that we are counting on,” Mariners manager Scott Servais said.

Let’s start with Paxton.

If this were football, James would be the receiver with 4.2 40 speed and a 39-inch vertical. His velocity did to scouts what Pavlov’s bell did to dogs.

In fact, according to FanGraphs, Paxton’s average fastball was 96.6 mph in his June 1 start vs. the Padres — which is the third-highest average in an MLB game this year (only Noah Syndergaard and Nathan Eovaldi have been better). And yet, he was taken out after 32/3 innings upon allowing 10 hits, three earned runs and eight runs total.

Since then, Paxton has had three quality starts, and two games in which he gave up at least four earned runs. His five-run, five-inning performance vs. St. Louis last week spiked his ERA to 4.15, although his strikeout rate and Fielding Independent Pitching suggests he’s throwing better than traditional stats would indicate.

“I’ve had some tough luck in some of these games,” Paxton said. “I’d like to see some better results.”

Don’t interpret that as Paxton blaming losses on misfortune alone. He knows there are things he can do better, like develop his curveball into a more formidable pitch.

And when it comes to the notion that he and Walker must be on the frontline of the M’s resurgence, Paxton doesn’t disagree.

“I think this is definitely our time to come out and really help this team,” he said.

As the Mariners (41-39) sit two games out of the wild-card race, their reaching the playoffs may come down to their biggest wild card: Walker.

There have been stretches this year (such as all of April), in which Taijuan has looked like a Cy Young candidate, and others (such as all of May) in which he has been overmatched.

Sure, his 3.29 ERA is 11th in the American League, but that number is sullied by a slew of poor starts correlating with Seattle’s skid. And considering Walker has pitched six innings or more just three times since April 25, he’ll be the first to admit he has to be better.

“I think the biggest thing is that I had that bad month, especially being consistent going deep into games,” said Walker, who was 0-5 with a 4.91 ERA in May, and gave up six runs in six innings in his first June start. “The numbers that I really want are the innings. I see everyone’s up to 100 innings already, and I’m at 80 or whatever, (82, to be precise).”

To Walker’s credit, he has looked like his April self in his last two starts, giving up just one run in 111/3 innings. His four-hit performance in a win over Baltimore Thursday was particularly impressive.

But as Servais said, the difference between good pitchers and great pitchers in the big leagues is consistency, and that’s a quality that has eluded Walker in his second full-time MLB season.

There are still plenty of games, though. There is still time for these touted prospects to complete the transition to touted pitchers.

Few will dispute the fact that James Paxton and Taijuan Walker still have room to grow in their young careers. But they need to complete that growth soon, because the Mariners do not have room for error.