TAMPA, Fla. -- Up until last week's game against the San Francisco 49ers, the Tampa Bay Buccaneers hadn't seen the return on investment they were expecting from their 2018 draft class.

Defensive tackle Vita Vea, the Bucs' No. 12 pick, notched his second sack and three tackles for a loss against the 49ers, and strong safety Jordan Whitehead turned in a team-leading 11 tackles (10 solo) and two pass breakups, suggesting there is some hope with this rookie group after all.

Prior to his breakout performance, Vea had recorded just three tackles and one sack in eight games, a tough pill to swallow for Bucs fans who instead were clamoring for former Florida State's Derwin James. The Los Angeles Chargers drafted the safety at No. 17 and he is a strong contender for NFL Defensive Rookie of the Year.

Vea's pro career got off to a rough start when he missed all of training camp and the first three games of the regular season with a strained calf muscle. He also had to trim 15 pounds from his 347-pound frame, a concern for some teams ESPN spoke to prior to the draft.

He drew some comparisons to 6-foot-2, 345-pound Danny Shelton, whom the Cleveland Browns selected 12th overall out of Washington in 2016 but traded to the New England Patriots last year. In 46 games with the Browns, Shelton recorded 1.5 sacks.

Vea credits Sunday's performance, which included plowing through All-Pro offensive tackle Joe Staley, to "not thinking so hard" for the first time this season.

"I wasn't thinking; I was just playing," he said. "It's really just going out there and playing, just playing, letting loose. You've gotta keep it simple and stuff like that ... just running. They say good things happen when you're just running to the ball."

As for Whitehead, the Bucs' fourth-round pick, he has had to step up as the Bucs have been without starters Chris Conte (injured reserve) and Justin Evans (toe). Whitehead also was dealing with injuries, including a hamstring strain and a concussion, which he had to clear the protocol in a week's time in order to play last week.

"I thought Jordan played well overall," Tampa Bay coach Dirk Koetter said. "You know, we played a lot of man coverage, especially in the first half when we were in base defense against their 21 personnel. Jordan, not only was he down in the box as a run player, he was the primary guy covering [tight end George] Kittle, and I thought he really stayed close to Kittle for the most part. At least three times that I can remember when they were running those against-the-grain boots [roll-out passes], he was right there."

Over the past two weeks, Whitehead has led NFL rookies with 17 solo tackles. The Bucs were missing three starting linebackers and the 49ers were checking it down repeatedly, but Whitehead still had to put himself in position to make those tackles.

Another rookie pressed into action early has been cornerback Carlton Davis, a second-round draft pick who took over as a starter when Vernon Hargreaves went on injured reserve. Davis has had his share of injuries this season and has encountered some growing pains.

On one play Sunday, Davis was juked by Dante Pettis while lined up against Pettis in the slot. Pettis caught him guessing wrong with an inside release for a touchdown.

Davis also gave up a 41-yard catch to Odell Beckham Jr. two weeks ago. Against the Carolina Panthers, he drew a costly 15-yard penalty for taunting after getting in Devin Funchess' face after a fourth-down stop.

To make matters worse, Christian McCaffrey leaped over Davis during a 32-yard gain; and on the very next play, Davis surrendered a 32-yard gain on an end around by DJ Moore. Davis has three pass breakups and has yet to record an interception, but as the game starts to come to him, the hope is that he can use his physicality at the line of scrimmage and his length to counter the NFL's big-bodied targets.

As for the rest:

Cornerback M.J. Stewart has missed the past four games with a foot injury, but he also has had his share of rough moments, as has second-round running back Ronald Jones II with a hamstring injury. Prior to Jones' injury, he was a healthy scratch the first three games, and his longest run was for 9 yards against the Browns.

Offensive guard Alex Cappa, a third-round draft pick out of Humboldt State, saw his first game action last week and performed, according to Koetter, "like a guy getting his first NFL snaps." Meanwhile, wide receiver Justin Watson has primarily been used on special teams, the result of the Bucs' depth at the position.

Sixth-round pick Jack Cichy suffered a season-ending torn ACL against the Browns in Week 7.

Only one starter? It could be worse

Vea has three starts this season, Davis has 10 because of Hargreaves' injury and Whitehead has six because of Conte's injury. A closer look at other NFL teams' recent drafts (or even the Bucs' own 2016 class) suggests it could be worse.

In 2016, the Bucs had one starter emerging in Hargreaves, defensive end Noah Spence barely seeing the field and kicker Roberto Aguayo getting cut after one season.

Injuries wiped out the Patriots' four-person draft class in 2014.

Of the New York Jets' picks through the first four rounds in 2014, just one remains on the roster.

The Philadelphia Eagles' first three picks in the 2011 draft -- guard Danny Watkins, safety Jaiquawn Jarrett and cornerback Curtis Marsh -- combined for just 20 starts in three seasons.

The Browns had nine first-round draft picks from 2011 through 2016. Not one is on the team.

So while Tampa Bay's pedestrian production from its 2018 class is not ideal, it is far from a worst-case scenario.

ESPN's Mike Reiss, Tim McManus, Rich Cimini, Turron Davenport and Patrick McManamon contributed to this report.