SANTA CLARA — The 49ers front office unceremoniously got rid of another vestige of the old regime as the Faithful celebrated the beginning of a new era on Tuesday.

The Niners flipped 2016 fourth-round pick Rashard Robinson for a fifth rounder in the 2018 draft. The move represented how fall Robinson had fallen since entering the season as the top cornerback on the depth chart.

“It wasn’t an easy decision,” head coach Kyle Shanahan said Wednesday.

Ultimately, the 49ers valued draft picks so much, they couldn’t pass on an opportunity to add one in the fifth after losing theirs in the Vance McDonald trade.

Making the decision easier — in addition to Robinson’s penalty problems — was Ahkello Witherspoon’s strong play on Sunday against the Philadelphia Eagles. Witherspoon, a third-round pick in 2016, made an impressive athletic play to intercept Carson Wentz.

“We thought he played well. Hoping he gets better as this goes,” Shanahan said. “Knowing that he was starting definitely makes it easier.”

Witherspoon and Robinson were friends in the locker room. And Tuesday’s move was the first lesson for the rookie Witherspoon that your pals in the NFL can be there today and gone tomorrow.

“I think highly of him as a player, period,” Witherspoon said of Robinson. “I’m not going to pretend about that. So to see [him traded] is a shock.”

For now, Witherspoon will take the vote of confidence from his coaches and focus on improving the mental side of his game.

He said he misread the play when he allowed a touchdown against the Eagles, but that he’s going to grow from the mistake.

How does he plan to go about that?

“Try and go for two picks next time,” Witherspoon said.

jpalmer@sfexaminer.com