BACKGROUND AND AIMS: The association between acute-phase blood pressure (BP) and outcomes in watershed infarction (WI) remains unclear. This study aimed to investigate the relationships between BP and BP changes with neurological functional decline (NFD) and functional outcome at 90 days. METHODS: We included patients with WI from a prospective, observational, single-center study (Effect of Cardiac Function on Short-Term Functional Prognosis in Patients with Acute Ischemic Stroke, SPARK). We recorded data of systolic blood pressure (SBP) and diastolic blood pressure (DBP) on the day of admission, as well as on day 2 and day 3. In logistic regression models, both the baseline BP and BP changes were assessed. RESULTS: Among the 207 patients with WI, 147 (71%) had concurrent cortical and internal infarcts. After adjusting for relevant factors, higher baseline SBP (OR:1.17
95% CI:1.01-1.37) and DBP (OR:1.04
95% CI:1.01-1.09) were associated with an increased risk of NFD. However, the restricted cubic spline (RCS) curve indicated that this association was statistically significant only when SBP was >
180 mmHg or DBP was >
100 mmHg. Additionally, an elevation in DBP of ≥4 mmHg on day 3 was associated with a reduced risk (OR:0.28
95% CI: 0.08-0.97), whereas an elevation of DBP ≥10 mmHg was not. Neither baseline BP nor BP changes were associated with functional outcome. CONCLUSION: In patients with WI, the risk of NFD increases when baseline SBP >
180 mmHg or DBP >
100 mmHg. However, raising DBP by ≥4 mmHg but <
10 mmHg on day 3 is associated with a reduced risk of NFD. BP may not be associated with functional outcome. TRIAL REGISTRATION: https://www.chictr.org.cn/, ChiCTR2300067696.