For Spurs point guard Cory Joseph, the first rule of replacing an All-Star such as Tony Parker is easy enough.

Namely, forget trying to replace Tony Parker.

“I’ve got to be Cory Joseph,” said the 21-year-old Canada native. “I can’t do what Tony does. I just have to go in there and be myself.”

As recently as a week ago, Joseph was running the show for the Spurs’ Development League affiliate in Austin, thriving against the likes of the Idaho Stampede and Sioux Falls SkyForce.

Tonight at the AT&T Center, against a Chicago Bulls team boasting arguably the nastiest defense in the NBA, the former first-round draft choice is set for his second consecutive start for the big club.

With Parker out for up to four weeks with a left ankle sprain, how the Spurs respond without their leading scorer, assist man and catalyst will largely determine whether they hold on to the top spot in the Western Conference.

How Joseph handles the responsibility could chart the course for the rest of his NBA career.

“It’s not the easiest thing to do,” said Spurs guard Manu Ginobili, 14 years Joseph’s elder. “You’ve been in the D-League for a long time, and you know you have this huge opportunity with Tony out for a month. So, you’ve got to be ready.”

Spurs coach Gregg Popovich named Joseph — a second-year player out of Texas with 39 games of NBA experience to that point — the substitute starter before Sunday’s 114-75 victory over Detroit.

Popovich chose him over fourth-year pro Patty Mills and rookie Nando De Colo, both of whom owned more career starts than Joseph’s one.

The 6-foot-3 Joseph was solid enough against the Pistons, scoring eight points with four assists. He was active on defense and, most important, surrendered only one turnover.

“He’s improved a lot the couple of years he’s played down in the D-League,” Popovich said. “He’s gotten his opportunity, and he seems to be taking advantage of it.”