Top seed Lumsden followed up her impressive semi-final win over Lucia Rizza to beat Natasha Fourouclas by the same score (6-2, 6-0) in Sunday afternoon's women's singles final.
Shortly after, Rosenzweig – second seed in the men's draw – had enough left in the tank following his three-set success over wildcard Johannus Monday in the semi-final to surge to a stunning 6-2, 6-1 win over top seed James Mackinlay in the men's singles final.
Mackinlay at least enjoyed some revenge when pairing with Patrick Young to overcome Rosenzweig and Euan McGinn in the men's doubles final, edging a tight contest 6-4, 7-5.
Meanwhile, Rizza and Rosie Sterk ensured a wide spread of silverware when they defeated Eilidh Mclaughlin and Zoe Moffat 6-3, 6-3 in the women's doubles final.
Afterwards, Lumsden reflected on her latest achievement of a superb run of form in the final months of 2018, after she won her first ITF $25,000 tournament in Shrewsbury last month.
She said: "I'm really happy, it's always nice to win tournaments and I played some good matches today. It's a great feeling to be national champion, that's a big honour. I've been training very hard over the last few weeks so when you have these winning moments it shows it's paying off."
The culmination of the enhanced Tennis Scotland Open Tour 2018, the Masters is the finale of the new nationwide progressive tournament structure which returned for a second year after the fantastic success of the pilot in 2017.
Tennis Scotland CEO Blane Dodds said: "Huge congratulations to Maia and Nic for their fantastic wins in the singles today and to Lucia, Rosie, James and Patrick for their doubles successes as well.
"On behalf of Tennis Scotland I'd like to thank all players, coaches, staff and volunteers who have helped provide a superb weekend of tennis and also to all the families, friends and fans of Scottish tennis for supporting.
"The enhancements we have made with the new format of this Masters series of events have been very well received by players and we're committed to continuing that innovation and investment to further grow this event and others in 2019."
All tournament information results can be viewed at: https://bit.ly/2QLV2JP