CHICAGO -- Alfonso Rivas joined the Cubs' system when the organization was still fielding a star-packed roster with October aspirations. He arrived to the big leagues under much different circumstances.

Rivas was summoned from Triple-A Iowa with a chance to show how he might fit into the Cubs' puzzle as they plan for the future in this post-Trade Deadline transition period. In his MLB debut on Sunday, he collected a pair of hits within a tough 13-1 loss to the White Sox.

"It definitely makes you put your head down and get to work," said Rivas of the opportunity at hand. "You definitely want to be the next guy up. You want to be the guy that the team relies on. I'm excited to be that person. I'm definitely going to work towards being that person."

Right now, the Cubs are focusing on development moments in a stretch of games that have included a heap of defeats. In Sunday's loss, rotation leader Kyle Hendricks (eight runs in 4 2/3 innings) was uncharacteristically roughed up, but it was nonetheless a memorable day for Rivas.

The stripping-down of the roster at the Deadline paved the way for an opportunity for someone like the 24-year-old Rivas. He came up from Iowa on Saturday, alongside reliever Scott Effross. They both made their debuts on Sunday, becoming the 62nd and 63rd players used (extending a club record) this year.

"I think it's healthy for the space we're in, where it's real opportunities for guys," manager David Ross said. "That's exciting for them, when guys get to come in, get called up and have a chance to make their mark in the Major Leagues."

In his first Major League at-bat, Rivas wasted no time, swinging at a first-pitch fastball from White Sox starter Dylan Cease. The pitch headed in at 98 mph and Rivas sent it up the middle for a one-out single to center in the third inning.

“You're talking about some real velocity,” Ross said. “Nice job jumping that first heater. His first at-bat, get that thing out of the way. And I thought he really managed the plate well.”

To Ross’ last point, Rivas took a more patient approach in the fifth, watching a curveball and changeup for strikes before taking a too-high heater to pull into a 1-2 count. Cease went with another curve over the outside edge, and Rivas slashed it down the left-field line for a double.

"I got to see him last Spring Training for the first time," Ross said. "It was really a controlled at-bat. He knows the strike zone, takes his walks, [makes] contact. He’s more of a gap-to-gap kind of player, but I really love the way he controls the zone.

"And his at-bats seem to be professional every single time. It's a calmer at-bat."

Rivas continued that "calmer" approach in the seventh, when he fought through a seven-pitch battle with setup man Ryan Tepera. Finally, Rivas sent a low slider deep into the left-center gap, where Sox center fielder Luis Robert robbed him with a running catch. Per Statcast, the play came with a 60 percent catch probability.

Effross looked to have more of the rookie “nerves” (as Ross phrased it) in his debut, allowing one of the five homers launched by the Sox. Robert took the sidearmer deep in the sixth, adding to the blowout.

Rivas -- acquired from the A's for utility man Tony Kemp in January of 2020 -- gave a glimpse at the MLB level of what he had been doing at Iowa.

In his last 18 games prior to the promotion, the lefty-swinging Rivas hit .364/.432/.439. He had a .284/.405/.411 slash line overall in 58 games on the season with 17 extra-base hits and 35 walks to 49 strikeouts.

"That's kind of been my game -- be a hitter first, rather than just start launching balls," Rivas said. "That's something I take pride in. I'm really focused on every pitch -- strike zone discipline and all that stuff."

Even in the midst of the loss, Hendricks said there was still an appreciation for seeing two more prospects get their first taste of the Majors.

“Absolutely, man,” Hendricks said. “It was awesome to see. It's a special moment in this game. Special moment for those guys. And [for Rivas] to get a knock his first and second AB, it's just a really cool day. It's something they'll always remember. It's just cool to watch from the outside.”