SCOTTSDALE, Ariz. -- Much more goes into a team's Opening Day roster decision-making than looking at statistics compiled in Spring Training games. But when there is a true competition for a vacancy, the on-field results can certainly offer a tiebreaker.

The Cubs have been spending this spring evaluating Hayden Wesneski, Javier Assad and Adrian Sampson for the lone job available in the rotation. Wesneski has impressed in his spring outings and Assad has opened eyes in the World Baseball Classic, while Sampson had struggled early on to find his footing.

"I think it's important for him and for us and for everybody out here," Cubs manager David Ross said of Sampson, "when you're competing for a spot, it's important to go out there and show what you can do and show why you belong on the team."

In a 5-1 loss to the Giants on Saturday, Sampson took a step forward with a solid performance, pitching into the fifth inning in his latest bid for a rotation role. In light of his showing, here is the latest on how things are shaping up around one of Chicago's remaining roster battles.

1. Sampson gets back to strengths

The most important number in Sampson's pitching line against San Francisco was zero home runs allowed. The righty had surrendered eight shots in 8 1/3 innings going into the outing, but on Saturday he kept the ball on the ground for much of his 4 1/3 innings at Scottsdale Stadium.

"Today, the separation with the four-seam and two-seam was very evident," Cubs catcher Tucker Barnhart said.

After earlier games this spring, Sampson noted that some mechanical issues were hindering the movement on his two fastballs, resulting in too many pitches left over the plate. Against the Giants, however, he generated five ground balls, struck out six and the lone out in the air was a fly ball to shallow center.

Overall, the performance from the 31-year-old Sampson resembled the body of work compiled last year, when he had a 3.11 ERA in 104 1/3 innings and a 1.71 ERA in his last eight turns. The Cubs will weigh that history against Sampson's spring performance as they consider the rotation makeup.

"I'm trending in the right direction," Sampson said. "There’s still little stuff to clean up, but today was a great outing."

2. Assad a fit for rotation or bullpen

Early Saturday morning, Cubs second baseman Nico Hoerner was chatting with pitchers Adbert Alzolay and Manuel Rodríguez about what Assad has been doing for Mexico in the Classic.

"How hard is he throwing?" Hoerner asked.

"He got up to 97," Alzolay replied.

Indeed, Assad reached 96.8 mph on a strikeout pitch to slugger Pete Alonso in a jaw-dropping three-inning outing against Team USA last weekend. Then, on Friday, the righty worked 2 2/3 impressive frames in Mexico's comeback win over Puerto Rico.

Between Cactus League play and the Classic this spring, Assad has turned in 9 2/3 shutout innings with eight strikeouts and two walks. Assad has allowed just two hits -- a single apiece to superstars Mike Trout and Francisco Lindor. The pitcher held the United States and Puerto Rico to a 2-for-19 showing combined.

It has been the type of performance that could net Assad a multi-inning relief job, if the rotation job goes to someone else.

"He's in the mix for being on the team," Ross said. "I think that's all that matters to him. It doesn't matter whether it's starting or relieving. When he's pitching like that, he can really help us."

3. A lesson learned for Wesneski

After Wesneski's latest spring start on Friday, the rookie pitcher admitted to a lapse in focus on the mound. In his fourth inning against the Dodgers, a leadoff walk was followed by a single and then a mistake pitch for a home run off the bat of slugger J.D. Martinez.

Even so, Wesneski, the Cubs' No. 5 prospect per MLB Pipeline, has looked like a favorite for the No. 5 spot this spring, with 17 strikeouts against four walks in 12 innings.

"I just need to lock in a little bit more," said Wesneski, who had a 2.18 ERA in 33 innings for the Cubs late last season. "It's still Spring Training. We're still figuring it out. I'm not happy about it, but we're going to work through some things."

Wesneski was tough on himself, but Ross said it was the type of spring outing that can lead to some lessons for a young pitcher.

"If you go back and look at the at-bats before that [homer]," Ross said, "that's where he could have ended the outing. And I think that's where he should be hard on himself on that, because that's what's going to make the difference in the season of winning and losing ballgames.

"But having a rough outing like that, and knowing where you can really hone in and focus, is a good thing to me."