Australian legend Karrie Webb has a big chance to become the first player to win back-to-back Senior LPGA Championship titles as she shares second place going into the final round in Jasper, Indiana.

The seven-time major champion posted a four-under 68 second round on a marathon Friday, having already completed the last 14 holes of her opening 71 after bad weather interrupted day one.

Webb is three shots behind England's Trish Johnson, who carded a second-round 66 to get to eight under as she pursues a third Senior LPGA Championship crown.

Last year Webb triumphed at her first appearance in the event after going head to head with her great career rival Annika Sorentam for three days and breaking the championship scoring record by six shots at Salina Country Club.

Defending a title is nothing new for the 48-year-old Queenslander, who won 41 times on the regular LPGA Tour with 15 more titles worldwide. She successfully defended five of those wins.

But she acknowledged the Sultans Run course used this time presented a difficult test.

"I don't remember the last time I played 32 holes in a day," said Webb.

"I'm glad we had carts because it's hot and this course is a challenge for sure.

"Trish made a lot of putts and I just didn't want to fall too far behind."

Johnson was wary of the threat posed by Webb and Becky Morgan of Wales, who shares second place with the Aussie.

"I am not counting any of my chickens at all," said Johnson.

"I am just going to go and put out another low round because the more Webby plays, the better she gets, so I need to get to at least 10 under.

"I am just going to have to play good again tomorrow."