Victory for Boulter comes as she battles to maintain the British primary rating with Emma Raducanu and Sonay Kartal closing in.
Boulter has been the nation’s main ladies’s participant since June 2023, however has dropped down the world rankings in a stop-start season.
Raducanu is as much as forty ninth after reaching the Miami quarter-finals final month, whereas Kartal’s fast rise has moved her as much as sixtieth.
Each play their Madrid first-round matches on Wednesday.
“I do not really feel any strain in any respect,” Boulter advised BBC Sport earlier than beating Siniakova.
“I am very comfy within the seat that I’m and I do know that each single particular person has a special journey and my journey isn’t going to be in comparison with anybody else’s – I am pleased with that.
“I have been the British primary for 2 years, it has been a good whereas now. It is one thing which I am fairly used to.”
After profitable one and dropping one in every of her Billie Jean King Cup singles matches final week on indoor clay within the Netherlands, Boulter went to Alicante – the place her fiance Alex de Minaur has lengthy been based mostly – for a coaching week.
She determined that was the wise choice – as a substitute of compacting in one other WTA clay-court occasion earlier than Madrid – as she continues to handle a foot harm.
The difficulty has left her solely in a position to play 5 tournaments this season, lacking virtually two months of the WTA Tour between the Australian Open in January and Indian Wells in March.
“I wish to see the ladies going greater and better [in the rankings], however personally I’ve my very own targets and attempt to deal with these loads,” added Boulter, who secured GB’s place within the Billie Jean King Cup Finals alongside Jodie Burrage within the deciding doubles.
“For me I simply have to attempt to keep wholesome. That is that the majority necessary factor after which the rating will handle itself.”
