MELBOURNE, Australia—Maybe, just maybe, the thinking went, Novak Djokovic would be just a tad more susceptible to trouble this time around at the Australian Open. After all, he wrenched his midsection during a slip in the third round and said he’d torn a muscle. Entering Sunday, Djokovic already ceded five sets in the tournament, the most he ever dropped en route to a major final. And he was facing Daniil Medvedev, owner of a 20-match winning streak. Yeah, right. We’re talking about Djokovic at Melbourne Park, where his dominance is most certainly intact—nine finals, nine championships. Plus, he’s still gaining on Roger Federer and Rafael Nadal in the Grand Slam standings, now up to 18 overall, two shy of the men’s record those rivals share. Djokovic used superb serving, his usual relentless returning and baseline excellence to grab 11 of 13 games in one stretch and beat Medvedev 7–5, 6–2, …