Complex sentence: Future champion Juan Martín del Potro made his first appearance in the main draw of the US Open, and this was also the first Grand Slam tournament of future World No.1 Novak Djokovic was seeded.
Split into simpler sentences: Future champion Juan Martín del Potro made his first appearance in the main draw of the US Open. This was also the first Grand Slam tournament in which future World No.1 Novak Djokovic was seeded.