Both strikers are likely to come under more scrutiny in recent weeks after Harry Kane picked up an ankle injury, with Son being chosen to replace the England international from the start at White Hart Lane before Janssen came on as a second-half sub.
"[Janssen] will now have the possibility to play more and be more involved. Today showed great, great energy when he came on," he told reporters.
"I think [Son's performance] was good. He had some chances to score and showed some great movement behind the defensive line. He worked well with Dele and Christian and I am very pleased with his performance."
Son has scored seven goals in 24 Premier League appearances this season, while Janssen has managed just one in 20 - although the vast majority of those have come off the bench.