SAN DIEGO -- Jon Rahm is not letting his withdrawal from the Memorial Tournament and subsequent isolation impact his positive attitude heading into this week's U.S. Open.

He also said he wished he had been vaccinated sooner. 

The third-ranked golfer in the world said he was playing some of the best golf of his life when he got pulled from the tournament because of a positive COVID-19 test, and he said there's no reason he won't continue that trend, even with less preparation this week at Torrey Pines.

"When you don't hit a golf shot for just about a week, it's tough leading into a major, especially a U.S. Open,'' Rahm said Tuesday after a practice round. "I'm confident I can get in form quick enough. ... I still have the memory of all those great golf shots I played, right? I'm going to choose to remember that. I've been playing really good golf all year. Two weeks ago, it's finally clicking all together like I was waiting for it to happen. Finally everything was firing on all cylinders. Not that I'm expecting to play that perfect again, but I know that I can play at a really high level. So I'm confident.''

Rahm explained that he received the COVID-19 vaccine prior to the Memorial Tournament, but he was still within the 14-day window following the shot and thus not considered fully vaccinated. As a result, he was not exempt from the PGA Tour's contact tracing protocols and was therefore required to be tested daily after coming in close contact with someone who contracted the virus.

After five days of negative tests, Rahm tested positive Saturday while holding a 6-stroke lead at Muirfield Village. He was informed coming off the green that he would be forced to withdraw from the tournament.

"Looking back on it, yeah, I guess I wish I would have done it earlier, but thinking on scheduling purposes and having the PGA and defending Memorial, I was just -- to be honest, it wasn't in my mind,'' Rahm said of getting vaccinated. "I'm not going to lie, I was trying to just get ready for a golf tournament. If I had done it a few days earlier, probably we wouldn't be having these conversations right now. It is what it is. We move on.''

Rahm said he took another test afterward that was also positive, and he was allowed to return to his Arizona home via the equivalent of an air ambulance and then was forced to isolate from others. He was allowed to leave isolation once he had two negative tests, taken at least 24 hours apart. His first negative test came last Thursday, and when he got the results of the second test on Saturday morning, he was allowed to start hitting balls again.

"I was a little bit scared because, even though I was feeling fine, I didn't want to give the virus to anybody in my house,'' Rahm said. "I didn't want to possibly give it to our young son [born in April]. I think the hardest part out of all this was for just over 10 days not being able to even spend any time with my little one. Adding to that, my parents came into town, couldn't be around them. ... I wasn't there when my parents met my son, and I hadn't seen my parents in over a year, almost a year and a half.

"Those are the hard parts about this virus in life. Whatever happens on the golf course was absolutely secondary in my mind. For anybody wondering what was going through my mind, all that was going on because my parents landed Monday, Tuesday they met my son, and I wasn't there. That was truly, truly a hard thing.''

Rahm said he supported the PGA Tour's rules on players who were in his situation.

"I've heard a lot of different theories: I should have played alone; I shouldn't have -- that's nonsense,'' he said. "The rules are there, and it's clear. I'm not going to lie, I was fully aware when I was in tracing protocol that that was a possibility. I knew that could happen. I was hoping it wouldn't. I was playing like it's not going to, but I support what the PGA Tour did. It could have been handled a little bit better possibly, but they did what they had to do.''

Rahm was referencing being notified just off the 18th green that he had tested positive. It was similar to being told last July at the same tournament that he had committed a rules violation that would add a penalty stroke to his scorecard. He still won the tournament.

"That's the second time I get put on the spot on national TV on the same golf course on the same hole,'' he said. "For all those people wondering when I said, 'Not again,' that's exactly what I mean: Not again."

Rahm begins the first round of the U.S. Open on Thursday at 4:36 p.m. ET off the 10th tee with Marc Leishman and Patrick Reed.