SCOTTSDALE, Ariz. -- Clarifying their rotation picture a bit before their fast-approaching, season-opening trip to Tokyo, the A’s made the surprise move of optioning Daniel Mengden to Triple-A Las Vegas before a 6-3 loss to the Rockies on Monday.

On the heels of a strong finish to 2018, Mengden had been viewed as a strong candidate for the A’s fourth or fifth starting job. Instead, he will have to spend at least the first 10 days of the regular season in the Minors, unless he replaces an injured player on the active roster. The two-game Japan Opening Series against the Mariners counts as two days.

Mengden had a fourth Minor League option year because he exhausted his three option years prior to accruing five professional seasons. With a crowded field of rotation candidates, the A’s opted to take advantage of that extra option. Mengden had a 5.73 ERA in 11 exhibition innings this spring, but his 2.52 ERA in his last 25 innings of 2018 had made him one of the A’s better pitchers down the stretch.

“He probably didn’t have his best spring,” manager Bob Melvin said. “We like him a lot. He just won’t start with us at this point. He’s been demoted before, and he’s come back and responded. And at times he’s responded and been as good a starter as we’ve had. He’ll be back at some point in time, and we are trying to create some depth, as well.”

This leaves Frankie Montas, Aaron Brooks, Chris Bassitt and Jesus Luzardo, the A’s top prospect per MLB Pipeline, as the remaining combatants for the two open rotation spots behind Mike Fiers, Marco Estrada and Brett Anderson. Options could play a role in this decision, as well. Montas and Brooks are out of options, and Montas is considered a veritable lock for one spot. Bassitt has an option year remaining.

The choice could come down to delaying the start of Luzardo’s service clock or exposing Brooks to waivers. Or the A’s could keep both pitchers and employ Brooks out of the bullpen. Luzardo has been one of the best pitchers in the Cactus League, allowing only one earned run on six hits in 9 2/3 innings. Brooks, who starts Tuesday against the Padres, has given up six runs on 10 hits in nine innings.

Because of the unusual schedule associated with the Japan series, the A’s won’t necessarily need the third, fourth and fifth starters until the fifth, sixth and seventh games of the season. Fiers and Estrada have been announced as the starters for the two games against the Mariners in Tokyo.

Leadoff spot to be in flux

The last few days of Cactus League action are a window into what the A’s leadoff situation could look like.

For Monday’s game, it was the right-handed-hitting Ramon Laureano at No. 1 against the righty Jon Gray. The day before that, it had been the switch-hitting Robbie Grossman batting lefty against White Sox right-hander Lucas Giolito. In a split-squad game that same day, it was the right-handed-hitting Marcus Semien against Giants lefty Andrew Suarez.

“We’ll play a hot hand, and we’ll potentially do lefty-righty,” Melvin said. “Grossman’s done a lot of it against right-handed pitching. We’ve been known to flip the lineup around. The short answer is, yeah, there could be some changes as we go along.”

Melvin will again use Matt Chapman as his two-hole hitter and Khris Davis as his cleanup hitter. Matt Olson and Stephen Piscotty both could figure prominently in the No. 3 spot.

Worth noting

• Longtime A’s broadcaster Vince Cotroneo had a new radio partner Monday at Salt River Fields: his son, Dominic. An up-and-coming play-by-play voice for the Double-A Corpus Christi Hooks (Astros), Dominic did a full radio broadcast (on KTRB 860 AM) with his dad for the first time-- an experience that both men said was emotional.

“You want to see your life pass before your eyes?” the elder Cotroneo said. “I walked his sister down the aisle in November, and now this!”

• Melvin said Jurickson Profar has looked comfortable adjusting to life as a full-time second baseman and, despite hitting into some poor luck, has put up good at-bats. His consistently buoyant personality also has been a boon to the clubhouse.

“He was sick for two days, and I didn’t even know it,” Melvin said. “His demeanor never changes. The guys all love him and embrace him.”

Up next

Brooks will get the start opposite Jacob Nix in Tuesday’s 6:40 p.m. PT road date with the Padres in Peoria. Montas, Ryan Dull and Ryan Buchter are also scheduled to throw for the A’s.