SAN FRANCISCO — Jim Harbaugh's first NFL passes came 25 years ago under the "Monday Night Football" spotlight, when the Chicago Bears visited the 49ers in a late-season game ripe with playoff ramifications.
Harbaugh didn't enter until after halftime, and only after Bears fill-in starter Mike Tomczak had thrown four interceptions.
Like that 41-0 rout by the 49ers, turnovers are expected to dictate their silver anniversary rematch at Candlestick Park, where the 49ers (6-2-1) host the Bears (7-2) again on "Monday Night Football."
Two of the NFL's premier defenses will be on display, and the winner will have the inside track for a potential first-round bye in the NFC playoffs. The 49ers are allowing a league-low 14.1 points per game, and the Bears are yielding the second-fewest points (14.8).
"It's a huge game," said Harbaugh, the 49ers' second-year coach who still holds the Bears' records for most pass attempts and completions. "Everybody will be crowded in to watch it, to see how we respond, see how the Bears respond.
"The football world will be watching this one."
Harbaugh, of course, is long removed from his Bears tenure (1987-1993) and that Candlestick debut in which he completed 8 of 11 passes for 62 yards. More relevant now is Harbaugh's health after receiving treatment Thursday for an irregular heartbeat.
He said doctors have put no limitations on him and that he's "going about everything as normal."
A normal 49ers-Bears duel, if history is any indication, won't provide a stress-free workplace for Harbaugh.
The Bears have forced a league-high 30 turnovers, and their defense returned seven of those thefts for touchdowns.
Linebacker Brian Urlacher was the latest to score off an interception two week ago at Tennessee. Cornerback Charles Tillman and linebacker Lance Briggs each returned interceptions for touchdowns in back-to-back games last month.
"It starts with the coaching," Briggs said. "Every day in practice, they're saying, &‘Run to the ball. Get a strip. Pick the ball up. Sprint. Score a touchdown. Score a touchdown. Score. Score. Score.'
"You hear that enough years in a row, it just becomes natural, first-nature to do."
Bears coach Lovie Smith and defensive coordinator Rod Marinelli have instilled a consistent system that's spawned from their time on Tony Dungy's Tampa Bay staff in the late 1990s.
"They try to keep it simple," 49ers defensive coordinator Vic Fangio said, "and they get their good players playing fast."
The Bears' fast start has come against subpar competition. They're 1-2 against teams with winning records: beating Indianapolis in the season opener, losing four days later at Green Bay and falling last Sunday to Houston. The Bears will pit their fourth-ranked run defense against the 49ers' league-leading ground game featuring Frank Gore and Kendall Hunter, who've each lost only one fumble in 203 combined carries.
The Bears' secondary has had a say all season. Tim Jennings leads the NFL with eight interceptions, and Tillman leads the league with seven forced fumbles.
"When it comes to stripping the ball and punching it out, he is just so far ahead of everybody, it's not even funny," 49ers offensive coordinator Greg Roman of Tillman.