In the third minute, Leao cut inside on the wing 1-on-1 and then shot into the top left corner of the goal, which was arguably one of the best goals in Serie A this season. The whole process, the pace and the ability to create opportunities show that Leao is truly outstanding as the best winger and even the best player in Serie A. Although the Atlanta players knew that he might choose this way, they still couldn't stop him at all. 
This is ability. 
However, unsustainability is his main problem, as well as Milan's. After taking a 1-0 lead, Milan still have a certain advantage in terms of statistics, but it will be difficult to create such chances. After all, Atalanta's increased efforts and the rapid increase in the difficulty of breaking through have made it difficult for Milan to be familiar with this set of things, coupled with the difference in physical strength, Milan quickly lost the rhythm they wanted. 
Atalanta are waiting, they are betting on Milan's double game in a week, and there will be fitness problems. So the next equaliser, and making the most of the counter-attacks to create pressure, was Gasperini's strategy. Clearly, he was more successful than Pioli. 
In the last 25 minutes of the game, some of the close-ups of the game were interesting. The Milan players naturally disagreed with the 1-1 scoreline and wanted to press up and create chances to take the lead again. However, the reality is that there is only the heart and no power. Leao's breakthrough is still sharp, but after passing a few people on the other side, his teammates are still waiting in place. Christian Pulisic and Loftus-Cheek also wanted to rest more, and their performances and individual postures were not at the same level as before. This is especially true of Olivier Giroud, who has "finally" shown age-appropriate fatigue, not only making mistakes in defence (which is controversial) but also being unfocused in attack. 
Of course, the fatigue of the players is inevitable, and the same is true for Inter, who rotate 7-8 main players to ensure the stability of the squad. For Pioli, that is not the case. After all, he was a little scared by the difficulties caused by the last rotation and the accusations that sparked after the game. vs Atala Nature is still the main force on the safer, which also causes the problems mentioned above. It's a pity indeed. Naturally, this is the difference between Milan and Inter (to be precise, the gap): there is a problem with the manager's line-up, there is a very impractical situation in the purchase and selection of players by the management, and there seems to be no special arrangement for how to play when leading and when there is a gap in fitness. In general, the coach and the manager have dereliction of duty, and the score seems to be "appropriate" with reference to the ranking. 
After the game, many Milan fans were reflecting on why Inter were able to rotate and be in good shape. Just think about the purchase of Moussa, Chukwueze, Okafor, etc. in the summer transfer window, and few problems that can be brought up make Pioli very troubled. How can they rotate when they don't have available talent? **10,000 Fans Incentive Plan