Use a sharp knife and cutting board to cut the seedless watermelon into chunks, removing any uneven pieces for even blending.
Place the watermelon chunks into the blender, ensuring not to overfill to allow smooth processing. Add a squeeze of fresh lemon juice if desired.
Blend on high speed until the mixture is completely smooth and uniform, with a bright, vibrant red color and no large fruit pieces visible.
Position a fine mesh strainer or cheesecloth over a large bowl and pour the blended watermelon through to strain out pulp and seeds, pressing gently to extract maximum juice.
Once strained, transfer the clear watermelon juice to glasses. Serve immediately over ice or chilled for a refreshing drink.
