There are many protagonists and key role players in the Celtics-Hawks playoff series. But the actors with the most lines have been Celtics captain Paul Pierce and the Hawks’ Joe Johnson.

Going into Sunday’s Game 4, the Celtics hold a 2-1 advantage in what is turning into a shootout between Pierce and Johnson. Johnson has attempted the most shots (60) and Pierce is second (57); that is nearly a quarter of the 478 total attempts of both teams.

Johnson is shooting 35.0 percent and Pierce 35.1 percent, an indication of the ramped-up defending by both teams.

But a major difference in the series so far has been the Celtics’ ability to give Pierce a defensive break. At key points in the game, the Celtics assign Mickael Pietrus to Johnson, giving Pierce the freedom to roam defensively and get in position for transition offense.

Pietrus has been a bit player offensively; he has converted only two field goals in 64 minutes of playing time. But he has been given a major responsibility defensively.

“Obviously, you know, the offense is not going to be in my hands,’’ Pietrus said after Friday’s 90-84 overtime win. “I just try to give my team a lift, a better chance in the game, defensively. Try to bring something extra to the team.

“In the playoffs, defense is very important. I respect that. I know I can bring that. Sometimes I bring that, sometimes I’m not going to bring anything. Because we have Paul Pierce, KG [Kevin Garnett], and those guys are going to bring it. So I respect that.

“I’m going to help the team win the game. That’s why I enjoy playing with the team, rebounding, whatever. I enjoy playing with those guys, it’s a blessing being with them every day in practice.’’

“That’s why we got him,’’ said Celtics coach Doc Rivers. “The made shots are the gravy with him. He’s a terrific on-ball defender and that’s what he does. He has the ability to deny, get up into you.