Iginla signed a one-year deal with the Eastern Conference champion Boston Bruins on Friday night.
The longtime Calgary Flames and short-time Pittsburgh Penguins forward will make $1.8 million guaranteed and can make up to $6 million with Boston.
The Senators, refusing to settle after losing Alfredsson, responded with a bold move to acquire Bobby Ryan from the Anaheim Ducks.
NHL teams made a big splash on the first day of free agency with a slew of signings and some trades.
Less than a year after the league's latest lockout, many teams spent big bucks on free agents despite knowing they will have to deal with a smaller salary cap next season.
The Columbus Blue Jackets were among the big spenders, signing Nathan Horton to a $37.1 million, seven-year contract.