AKRON, Ohio -- The 36-hole lead was nice, and Jimmy Walker wasn't complaining. But he also wasn't celebrating, either. Sure, it was great to be out in front at the WGC-Bridgestone Invitational, but plenty of golf remained.

And while that might sound like a cliché, Walker was speaking more from the perspective of a year spent dealing with the effects of Lyme disease and the inconsistency that it has brought to his golf game instead of the usual ups and downs experienced with tournament golf.

He also seemed to suggest what awaited him Saturday during the third round at Firestone Country Club.

"I don't know how I'll feel day to day,'' Walker said.

It has made his year as the reigning PGA Championship winner less than ideal, and Saturday offered up the perfect example. He took a 2-shot lead into the third round, then shot a front-side 41 that included two double-bogeys and dropped him out of the top 20.

The six-time PGA Tour winner was left to fight for his game while playing partner Thomas Pieters surged into the lead and ended up tied with two-time major champion Zach Johnson after 54 holes. Walker is 6 strokes back after shooting 74.

Jimmy Walker will defend his PGA Championship title next week at the Quail Hollow Club in Charlotte. He won his maiden major a year ago at Baltusrol in New Jersey. Gregory Shamus/Getty Images

Walker has just one top-10 finish in 2017 and has dropped to 39th in the world while trying to deal with the bacterial illness that he does not know how he contracted. Walker said he has not felt right since Thanksgiving, and was finally diagnosed -- he thought he had mononucleosis -- in April on the day prior to the first round of the Masters.

"I don't know of anybody that's got it that can really describe it to you, but it's just not fun,'' Walker said. "It puts you in a bad mood. You don't feel good. You feel awful, like a lot ...

"I've been very tired and fatigued and no strength and it comes and goes.''

Walker managed to shoot 5-under-par 65 on Friday despite a long day due to weather delays that had him feeling alternately good and bad. He led by 2 strokes over Pieters.

But Walker bogeyed the first hole Saturday, then added doubles at the sixth and eighth before finishing the front side with another bogey.

And that is how the year has gone. Walker, 38, has had difficulty maintaining any consistency or building momentum. His best finish is a tie for ninth at the Tournament of Champions in January, where a small field of 32 golfers convened.

A regimen of antibiotics that Walker has already undertaken might not be enough. In the meantime, he deals with what can be flu-like symptoms with supplements and anti-inflammatories.

Walker played well on Friday despite waking up with symptoms and then feeling ill again after his round.

"It's been such a hard year healthwise and he's doing the best he can,'' said Walker's wife, Erin.

Although he has missed just four cuts, Walker has not contended, either. He has chosen to fight through the illness and continue playing despite the fatigue he often feels. Walker likely hasn't been helped this week by having played last week at the European Open in Germany the week following a tie for 54th at The Open in England.

A year ago, Walker was fulfilling a lifelong dream in winning the PGA Championship at Baltusrol, holding off Jason Day in the process and earning a spot on what would become the victorious U.S. Ryder Cup team.

But he has not been able to build on that success because his illness has not allowed him to do so, making his time as PGA champ somewhat bittersweet.

"I've enjoyed it, I really have,'' he said. "That's something I'll always be able to take with me, major champion. It's very cool. I've never looked at this like, oh, poor me. This is just life and bad things happen sometimes, you've got to deal with it and that's all we're doing.

"I'm just glad that I'm feeling better, but there's still a lot of stuff that is lingering and hanging in there. I just hit weird shots on the golf course sometimes and just lose focus and concentration.

"I've really tried to step that up this week, really narrowing the focus because it can slip away pretty fast. I've been trying to leave tickets for somebody all week, and I just can't seem to remember to do it every dang day. That's the kind of stuff that happens.''

Walker gathered himself on the back nine, birdieing the 15th and 16th holes to at least make the round respectable.

"It's always important to have a good week,'' he said. "I haven't had too many this year. It's kind of rough. But things have been trending. Last week I hit the ball well, just didn't put anything together, but I've been making some putts and it's nice to see.''