Tostevin completed a silver-medal backstroke double at the long-course Lisbon International in Portugal, setting a new Guernsey record over 100m and more than justifying her selection as part of a 30-strong England South West team.
At just 16 years old, the Millfield School student rose to the challenge of swimming against senior-level opposition.
Tostevin’s biggest success came on day one as she improved her own island 100m back stroke record to 1min. 3.10sec., surpassing her mark from last year’s British Championships, for second behind the flying Rafaela Gomes Azevedo.
The Portuguese national record-holder and European junior medallist had surged to a new meet record of 1-01-50.
Over 50m on Sunday, Tostevin clinched another silver in clocking 29.98 behind the returning Azevedo, who continued her record-breaking ways.
Tostevin also placed ninth in two other ‘A’ finals – the 50 fly and 100 free – together with a solid fourth in the 50 free ‘B’ race.
She had another opportunity to shine in the 4x100m relays, where England South West excelled in taking top spot in the medley as well as freestyle silver.
Barracudas stalwart and previous head coach Alison Frankland is no stranger to the teenager’s hard work and feels that she thoroughly deserves her current success.
‘Tatiana is highly motivated and her success at this high level meet is as a result of her commitment and dedication to training,’ said Frankland.
‘She does come here quite often whenever she’s on school holiday and she comes and trains with the Barracudas and it’s always a pleasure to see her.’
Tostevin now has her sights set on the British Swimming Championships in April ahead of targeting returns to the Island and Commonwealth Games in the next two years.