Answer based on context:

In week 5, the Lions hosted a nationally televised primetime NFC North Division duel against the Chicago Bears. It was the first ever Monday Night Football game at Ford Field, the first MNF appearance for the Lions since 2001, and the first Monday night game in the city of Detroit since 1974. Neither team scored in the first quarter. In the second quarter, the Lions got an early lead with a 73-yard catch and run by Calvin Johnson. With this, Johnson became the first receiver in NFL history to record 9 touchdown catches in a season's first five games. The Bears got on the board with a 44-yard field goal by Robbie Gould, and took the lead with a 9-yard catch by Kellen Davis. After halftime, the Lions regained the lead and never gave it back. First came an 18-yard TD catch by Brandon Pettigrew. A few minutes later, Detroit's Jahvid Best ran in a TD from 88 yards out, the second longest touchdown run in franchise history. Each team scored a field goal in the fourth quarter: first one by Chicago from 49 yards out, then a 31-yarder by Jason Hanson that completed the scoring. With the win, the Lions also started 5-0 for the first time since 1956 and also snapped their 6-game losing streak against the Bears. Ford Field's record crowd of nearly 68,000 fans caused 9 false start penalties by the Bears.

How many touchdowns were scored during the first half?
2