Without difficulty
readily, with ease, effortlessly, facilely, simply, with no effort, with no apparent effort, without trouble, handily, evenly, regularly, steadily, efficiently, smoothly, dexterously, plainly, quickly, comfortably, calmly, coolly, surely, just like that*, hand over fist*, hands down*, with one hand tied behind one's back*, like nothing*, like walking on air*, without even trying*.
Antonyms laboriously, wearily, arduously.