(Reuters) - Aryna Sabalenka’s mind was full of doubts before playing Serena Williams for the first time at the Australian Open but the feisty Belarussian has vowed to be mentally much stronger going into her next contest against the 23-times Grand Slam winner. The strongly built Sabalenka finished 2020 with trophies at Ostrava and Linz and arrived in Melbourne for the year’s first Grand Slam after picking up her third straight title at a WTA 500 event in Abu Dhabi. Sabalenka did not drop a set in her first three rounds before going down in three against the 39-year-old American in the fourth last month. The 22-year-old showed plenty of steel to fight back from 4-1 down in the decider to level the match but her nerves finally gave way when she committed an array of errors while serving to stay in the match trailing 5-4. “I felt like I missed my opportunity because I feel like if you are coming back from 1-4 and you’re kind of feeling your game and you’re there, you’re fighting, you just have to take this opportunity,” Sabalenka told reporters in Doha on Monday. “I felt like mentally I was a little bit up and she was down. I would say it was not really smart mistakes from me. But it was good experience because I never played against these kind of champions like Serena. “And going on the court, I was kind of like thinking what’s going to happen, how she’s playing, what’s her power and all this stuff. Then I step in on the court and I understand, like, ‘wow, actually I can play her, I can beat her’.” Sabalenka, who will defend her Qatar Open title this week, managed to match Williams’s power from the baseline but felt her approach was not right. “I can guarantee that my mindset will be different going on the court,” the world number eight said. “I don’t know what’s going to happen on the court, but I know that my mindset will be much stronger than last time. “Now I know what to expect from her and now I know where her level is. I think, yeah, it will be different next time.”