Complex sentence: Martínez started his playing career with local club Club Deportivo Morón in 2000; after several seasons playing in the third division, he joined Arsenal de Sarandí of the top level.
Split into simpler sentences: Martínez started his playing career with local club Club Deportivo Morón in 2000. After several seasons playing in the third division, he joined Arsenal de Sarandí of the top level.