Harrington trailed No. 2 Mickelson by 3.39 points last week and is now just 2.02 points back. Tiger Woods remains a solid No. 1.
Sergio Garcia shared second place behind Harrington and moved up two spots to No. 4 in the new rankings. Vijay Singh fell a spot to five, while Henrik Stenson climbed five spots to No. 6.
Ernie Els slipped a pair to seventh, Stewart Cink moved up one to eighth and Geoff Ogilvy slid two to ninth.
Steve Stricker held steady in the 10th position, while Adam Scott tumbled three to 11th. Justin Rose jumped four positions to 12th with Jim Furyk behind Rose at No. 13.
Lee Westwood fell a pair of places to 14th and was followed by Anthony Kim, who was 15th again this week. K.J. Choi also fell two spots to 16th and was followed Kenny Perry and Trevor Immelman, who stayed put in 17th and 18th.
Rory Sabbatini and Miguel Angel Jimenez exchanged places with Sabbatini up to 19th this week.
Ben Curtis, who shared second with Garcia, soared 40 places to No. 37.