England were 52 for two at the close on Friday after the tourists won the toss and amassed 527 for seven declared in their first innings, a huge turnaround from their woeful performances with the bat in the second test defeat at Lord's.
Clarke, though, is fully aware that being 2-0 down in the five-test series, Australia's efforts could count for nothing at Old Trafford if they do not press home their advantage.
"It's about time, I guess," he said when asked about his highest score against England and first test ton at number four.
"I think the team should be extremely proud of the position we are in at the moment. But we have a lot of work ahead, the wicket is pretty flat and there's not much out there for the bowlers.
"(Our comeback) shows a lot of character. I'm pleased with the first two days but it is irrelevant if we don't win the test."
With England only needing a draw to take the Ashes for a third straight time, Clarke's men need to remove the home side's captain Alastair Cook (36 not out) on Saturday and stop him racking up the kind of huge scores he struck in the last tour Down Under.
Ever the perfectionist, Clarke was upset he did not snare Cook on 15 at slip late on day two when the opener edged Nathan Lyon onto wicketkeeper Brad Haddin's knee and the ball fell short of the Australia captain.
"I probably should have had Alastair Cook if I hadn't been sat on my heels," he told a news conference as he criticised his own batting, having resumed the day on 125 not out.
"I didn't feel that great today or yesterday at the crease. I'll be able to assess it more if we win this test match."
After the DRS drama on Thursday, when Australia's Usman Khawaja was twice given out despite not hitting the ball, Friday saw the returning David Warner review when he clearly edged and England's Tim Bresnan not review despite not getting a nick.
"My reaction was yes, I thought Davey hit it," said Clarke, who was at the other end. "In fairness to Davey, it also hit his pad at the same time."
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